Traveling to Bath from London-prebuy train tickets?

Yes, you should pre-buy if you want a cheaper fare. What's not clear from your post is when you mention 'customs', where you're arriving from. Airport, or Eurostar? And which airport? Customs you just walk through so it takes no time (unless you have something to declare), passport control is usually no more than 10 minutes via egates, assuming there's no egate meltdown. Generally I find the delay is waiting for luggage.

If it's Eurostar, UK passport control is in Paris, so you just walk off the train at St Pancras.

Customs is nothing if you have nothing to declare - just walk out the green door (red if you do). Immigration is the time user-upper, as is baggage claim. If you qualify, and if the egates are working, immigration can be fast. If you need a human it can take much longer.

What if your plane is late or rescheduled, or very early? If you buy cheaper Advance tickets which are tied to a specific train you have a problem because they are effectively non changeable and non refundable (you can but it costs most of the value of the ticket and you still have to buy one for the train you want.

Will you take the bus to Reading and get the train there? Or will you backtrack into London Paddington and get the train there?

If your journey coincided with the August Bank Holiday weekend (24, 25, 26 August) you may well be affected by rail line closures as bank holidays are prime repair and line closure times.

There isn't a big difference in price between Advance train specific and walk up fares-

Looking at a random date (Saturday 17 August)- Advance Fare via the Bus to Reading, then train is £40, walk up fully flexible fare is £54.40;

via the all train route (change at Hayes and Harlington) is £38.10 Advance or £47 Fully Flexible.

via Elizabeth Line to Paddington then train is £36.20 Advance or £54.10 walk up fully flexible.

If you use Heathrow Express to Paddington it is £52 Advance or £66.90 walk up fully flexible.

So any which way there is less than £15 difference between Advance and walk up tickets- which is small change.

In fact as you say "we" , even if this is your only UK rail journey, it will be worth while buying a Two Together Railcard for £30- which will save you 1/3 off all the above fares, if you buy the higher priced flexible tickets.

Just to be complete you could take a National Express bus from Heathrow, but the next one leaves at 1305, arriving at 1520- a long wait if your flight is on time and baggage collection/immigration works well.

Sorry I used the wrong word-customs. Last year I went to France and was surprised at the lines to get into the country. I wasn't sure if that's how it was in England as well. Our airport is Heathrow.
So we are getting our luggage at baggage claim, then heading to Paddington to get the train to Bath--there are 3 of us, my daughter her boyfriend and myself--buying ahead would be a good idea? Guesses to best time? (arrival of airplane at 1045)

thanks for the additional info.

as Stuart said yesterday,

via Elizabeth Line to Paddington then train is £36.20 Advance or £54.10 walk up fully flexible.

The difference on taking the next available train just as soon as you get to Paddington versus buying ahead, waiting for the exact train which has to be far enough after you are scheduled to land so that you don't miss it is you are late for ANY reason is £17.90 per person. Only you can decide if you'd rather risk it to save £17.90 per person or if you'd rather have it easy with no worries for that amount of money.

As there are three of you that changes things. You benefit from the Groupsave ticket where you all get 1/3rd off, so for the three of you a Super Off Peak Single Bath to Paddington costs a total of £82.95 (so about £28 each).

You don't need any kind of railcard, just book 3 people together and you should automatically be offered that fare.

That is valid on any train. If we allow 1 hour to clear the airport then 30 minutes to reach Paddington on the Elizabeth Line, that potentially puts you on the 1230 train from Paddington. I would book seats on the 1300 train, but if you get there sooner or later you are free to take any other train.

If you were really late that fare doesn't apply to the trains ex Paddington between 1600 and 1830.

Create an account with GWR then if you are late, you can reserve new seats on a later train (no extra cost) on your phone on the way from Heathrow to Paddington. An example it is now 1221 here, I can still book seats on the 1230 train on their website.

That's a way to annoy people sat on the train who have sat down thinking they have found vacant seats!!

PS- NIgel and I cross posted, sorry Nigel.

At Heathrow just buy 3 x Elizabeth line singles to Paddington from the machines at £12.20 each (or swipe your contactless cards on the gates- 1 card per person).

My memory of getting through Heathrow last July is that the official stuff (immigration) was fairly quick - but I swear our plane must have parked at the last possible gate because we walked for a WHILE. Factor in a bathroom break and it was probably 20 minutes before we got to Immigration, maybe a little more.

I know you asked about the train, but what about the bus direct from Heathrow to Bath? My parents took is last April and thought it was great. I believe they just paid the driver when they got on? Others can confirm is that's true. A quick look at National Express says the trip should be between 2h15 (direct) and 3h45 (change in Bristol). BUT - keep in mind that if you take the train, it will take about an hour to get from Heathrow to Paddington, and you'll be going in the opposite direction. As the Aerlingus ad at Hartford Airport used to read (paraphrasing), "In the time it takes you to get to Boston, you could be well over the Atlantic."

Thank you so much everyone-all these suggestions have been very helpful!
I am not opposed to the bus...the hotel we have in Bath is supposed to be fairly close to the train station, so i would need to figure that piece out...

depending on terminal Heathrow Express is about 20 minutes to Paddington, Elizabeth Line is about 31 to 33 minutes, somewhat less than an hour.

Thanks Nigel-I saw the Heathrow express was a possibility to paddington-looks quite doable. Then the train from Paddington to Bath just under 2 hours, which is better than the over 3 hr bus ride. Plus no figuring out how to get from Bus station to hotel.
Also, making a GWR account seems like an excellent way around any delays--thanks isn31c
This has been extremely helpful, so thanks so much everyone!

Hi Val

I included Heathrow Express for completeness as a previous post had said it would take an hour from Heathrow to Paddington, but it is only a little faster than Elizabeth Line and WAY more expensive.

Thanks Nigel-very helpful!

The coach service can be a very good option but its main disadvantage is the lower frequency which may not fit in well with your arrival time

FYI--in Bath, the train station and the bus station are next to each other.

Last year I took the Heathrow to Bath bus and it was quite a scenic ride through the countryside and towns. Link below has ways to travel to Bath.

https://www.rome2rio.com/map/Heathrow-England/Bath-Station