National Express Coach from Heathrow to Bath

You definitely need a later bus. You will have to go through immigration, possibly get baggage, use the restroom, walk from your terminal to the bus, etc. This could all take upwards of 2 hours depending on how many other international flights arrive at the same time.

Book the next coach. If you arrive early and/or get through immigration/passport control quickly and get to the central bus station before the 13:15 coach departs, National Express will allow you on board, subject to space availability.

Book the next coach. Been there done that. The Express Coach can also get caught it in traffic and be late.

Why not take the train to Bath? You can take the train from the airport into Paddington then catch a train to Bath. There is an express train and a slower commuter train that you can choose. That way you won't get caught up in the traffic that a bus would.

If you want to take the train, you don't have to go into London. Take a Railair coach from LHR to Reading. Great Western trains from Paddington to Bath Spa stop at Reading.

Thank you for your responses. My gut was telling me to book the later bus and you all have confirmed that. Miss B, thought train option would be less direct than coach, and potentially take more time and cost more, but it is probably a good idea to explore that option further to confirm. Thank you.

If you arrive at Terminal 3, it takes about 10 minutes to walk to the Central Bus Station. You can take a trolley (cart)
for your luggage which is a blessing. The route is in an underground tunnel. I highly recommend the Railair bus to Reading Station (about an hour) which run every half hour. I use it all the time.
No advamnce reservations needed although you do need to buy a ticket before boarding.

NEVER makae a reservation for a flight, bus, etc. so close to your arrival time.
Heathrow is one of the busiest airpots in the world. The chances of landing on time are slim. Then you have to walk miles to go through immigration(and wait in LONG lines)and then proceed to the
baggage area if you have checked bags.
The easiest and fastest bit is Customs..you just walk through the part marked nothing to declare!

Thank you, Tim and Maryann, for your tips on Rail Air. Researching that option now. We fly into Terminal 5 so I like that they have buses that leave from there, instead of schlepping to Central Bus Station.