LHR T5 to Cambridge on National Express bus advise...

The next available bus (given that you stand no chance of making the 0715 unless the flight is very early) is the 0855. For an on time arrival that should be easily attainable, barring a big issue at immigration and major issues with checked bags.

This morning at least there was only 1 seat left on that 0855 bus when I checked at 0700. Thus without being pre-booked "we" would not have caught that bus if just arriving on spec.

You can choose "change and go" for an extra £5 to be on a later bus. They have now changed the scheme- previously it had to be done by 'phone or at a staffed bus station. Now, apparently, it can be done on line in the 'My Account' part of the Nat Ex website.
So you would need data or the airport free wi-fi.
But there are no guarantees (it is not a 'skip the line' scheme) that the next bus (at 1045, then 1245) will not also be charted full. As of 0900 neither is, today, and it would seem unlikely but is always a chance.

Any reserved seats are only carried over to a later bus under "change and go" if they are available (only the 1st 5 rows are reserveable), and the seat reservation fee is non refundable if not available on a later bus.

The 0855 bus will be showing a destination of 'University of East Anglia', the later buses 'Great Yarmouth'.

Everything is well signed at LHR- the bus leaves from the Arrivals forecourt at T5.

whilst settling in to the coach seats if those issues don't occur will be comfy and relaxing (it is a National Express coach after all), you might find the stress of worrying about the issues a worry.

Although it is a bit more work, taking the Elizabeth Line from T5 right to London Liverpool Street station, then an easy change onto the Greater Anglia train to Cambridge would have guaranteed seats on both segments. Even though you will run through the tail of the rush hour (what day of the week for your 7am arrival??) at both Liverpool Street and Terminal 5 you will be where the train starts and all seats will be available to choose from, and you will be leaving London from Liverpool Street against the flow.

You may prefer the coach but you should know the alternative. There are also other alternatives like Elizabeth Line to Farrington, change for one stop to St Pancras, (or if the train is a Cambridge one, stay on) walk across the street to Kings Cross and take the fastest train to Cambridge, but via Liverpool Street is the simplest train combo.

Thank you for your information and help! I definitely need to think about the choices.

We get in on a Monday morning. I read somewhere that there may be a potential tube strike in October. Is there any news yet about that?

There is no news on the potential tube strike- at least 14 days notice has to be given so 17 October is currently the earliest possible date (or Monday 21 October is the earliest possible Monday for a strike)

Nigel is giving excellent advice. We just made the Heathrow to Cambridge trip a few weeks ago and our plan was to use National Express. Unfortunately, we missed one coach by only a few minutes and the next was fully booked. You can check if seats are available on their app. We had already considered the options Nigel suggested, so we just took the Elizabeth Line into Liverpool Street Station and then purchased tickets on Greater Anglia. That option takes a bit more effort than National Express, but the Underground and trains to Cambridge run more frequently so we weren't left sitting around waiting for transportation. One bonus for us: the Cambridge station was closer to our hotel than the National Express drop off point.

Thank you for that advise... I was a bit worried about the bus being full. At least we'll have another option now and it is a relief after a long haul flight!

By the way the train and the bus are about the same price.

The Bus is around £34.

The Elizabeth Line to Liverpool Street is £13.30.

The maximum possible fare you can pay on a weekday from Liverpool Street to Cambridge is £28.10 Anytime Day Single before 0900 (you are unlikely to be there so early) or £26.10 Off Peak Day Singe after 9am.

In practice, even if it sounds an Oxymoron, there will almost always be a train specific Advance Single at about £21 for the next train out- these are usually sold until 2 minutes before train departure.

At a weekend there is a super off peak single available on all trains at £17- the maximum possible fare.

Those fares are less than on the Thameslink and Great Northern trains from Kings Cross or Farringdon (£30.50 and £31.50 respectively).

Thank you for the prices!