Should i take Eurostar to CDG or AMS to negate the higher airport fees at Heathrow?

I think I would only consider repositioning to Paris if I wanted to spend some time in Paris (which I would). Otherwise swallow the added fees and fly home directly.

I don't know what the order of magnitude is, but honestly this feels like "penny wise, pound foolish".

Why on earth go round the houses when there is the Carousel Buses #102 fast and direct bus running frequently 24/7 from High Wycombe to Heathrow direct then a direct flight to Dubai?

An easy straightforward journey.

If you fly from LHR or LGW to CDG or AMS you are still paying the airport fees- they are just baked into the ticket price.

Eurostar has 2 fleets of trains- the Class 373's and the 374's. The 374's date from c2015- how many planes you fly are more than 9 years old? How often does anyone write a review that says "my train ran on time today, a normal journey"? No- people write reviews when they have a grumble.

You might get either on any given day or journey.

No one builds a new train fleet every 9 years, but Eurostar have an order in currently for a new fleet to replace the older, 373's and also increase the overall fleet size substantially,

I would not take the Eurostar or a positioning flight to Paris or Amsterdam on the same day as my flight to Dubai on a separate ticket. There are a number of issues that could happen that would prevent you from making the flight.

How much will you really be saving after you have to pay for Eurostar and a hotel room?

How much will you really be saving after paying for a positioning flight and a hotel room?

I agree this is penny wise, pound foolish.

Why is the Eurostar "scary"? I took it to Paris last year and it was quite pleasant- immigration for France is at St Pancras and you just walk off the train at the other end. Nothing painful about it - all very quick.

But I agree there won't be much if any savings by the time you've paid for the train (or a flight to Paris or Amsterdam) and you'll have wasted a whole lot pf time.

Eurostar is simply a train, fairly comfortable. Who writes a good review of a fairly comfortable train?

However, you do now need to turn up around 90 minutes ahead of time in order to go through passport control, and the waiting area can be very crowded.

So it’s a bit of a hassle.

Also there are occasions when the line gets blocked, and that can be a nightmare as there’s not exactly another route the trains can take.

I’ve done (or tried to do) Eurostar for three trips. The first was painless. The second, all trains were cancelled all day due to someone throwing themselves on the tracks so I booked a last-minute flight instead. The third, arrived 90 minutes early as instructed, sat around in a crowded waiting room for more than an hour, but the train journey was easy and comfortable.

So it’s great (but not without some hassles) if you want to go direct between London and Paris/Brussels but it’s a hassle if you’re trying to do it just to save a few quid.

Fly from Heathrow. Quicker, simpler and fewer moving parts to go wrong.

Yup, "penny wise, pound foolish".

Forget the airport fees and taxes, what will you actually pay and what is the real difference you'll actually pay to fly from LHR vs flying from AMS/CDG? How much would you have to spend to take advantage that difference? After all the effort to reposition yourself is the money, time, and resources really worth it?

Usually going to somewhere else in Western Europe to take a long haul flight is worth doing if you are planning a flight in business or first as the difference in base cost plus added fees is significant enough to make a real difference. Currently I think Oslo is the recommended location but that changes regularly and can be different for different final destinations. The savings can often be in the thousands. But I don't think it's worth doing if you're flying economy.

But in truth only you know the actual numbers involved and maybe in your case you feel it is worth it. If so, I would want to be wherever you choose to fly from the day before, whether you fly or take a train. That inevitably means the extra cost of a hotel but again that can be a positive if it gives you some time in that city.

Dublin is usually cheaper than Paris or Amsterdam as a starting point if you only want a short positioning journey first but you have to check if this is so for your particular dates etc. Also consider going via somewhere which might interest you for a short stay.

Definitely fly out of LHR. It in not very efficient to time or cost wise to go to AMS or CDG. Way too many moving parts.

with the Brexit requirements

Maybe others have thoughts, but Brexit really did nothing to add requirements to the trip. Passport control was always required, as the UK was never part of Schengen. I suppose if you are a UK or Schengen area country passport holders, the process formalized a bit, but for the rest of us, nope.

I suppose there might be some customs hassles, but on my trip earlier this year (went round trip Brussels to London) I do not recall any.

I would not have concerns about taking the Eurostar, however, like others, I question spending money for the train ticket, a night at a hotel, meals, and other misc. costs; plus my time, all to save maybe $200 on a reward ticket? Seems like the costs will be much more. Working it in to a longer trip where I was going to be in Paris or Amsterdam anyway? Sure, but as a tactic to avoid a fee? No.

The UK fees are (much) higher if you are flying in a premium cabin vs economy. Since OP
does not indicate what cabin they want to redeem in, the full "business case" for one option
vs the other isn't clear.

I did this exact thing a few weeks ago; took a short flight from EDI to AMS and flew back to
the US from AMS. OP also does not say where final destination is; it is possible (as it was
for me) that the miles required for the flight out of AMS were a lot less than from EDI. So
savings in both miles as well as $, which again affects the evaluation. I definitely saved a
lot by doing this.

I do agree with the concerns about flying the 1st leg (on a separate ticket) on the same day
as the major leg, but that is a risk OP needs to decide on. Since they have indicated they
have flexibility with time, going a day earlier to CDG/AMS/wherever would mitigate those
concerns, which I did.

Thank you everyone for your inputs, indeed it seems better to visit somewhere i have never been for the positioning flight.
I had always wanted to visit parts of Ireland, so i will get myself there & spend a week exploring b4 flying out thro Dublin.

My redemption flight is for business class to SG, it probably works out the same in terms of money but i think a week in Dublin is a good start to longer trips in the future. I read that there is a Rail & Sail option from London to Dublin that sounds very interesting as i do prefer to take a slower mode of transport, i will research more & will be back here to get inputs for my travels thro England, Scotland & Dublin.

A sail rail ticket from High Wycombe to Dublin is £48.20 via Birmingham (leave HW at 0657, arrive Dublin 17:25).
You have a short walk between Birmingham Moor Street and New Street;
or £57.50 via London (the fare includes the tube from Marylebone to Euston, same arrival time at Dublin.

There is also an overnight option arriving Dublin at 6am, all fares include the ferry ride so are a huge bargain.