My first visit to the UK, I stayed in London and ventured out from there. So, living in Chicago, using the trains and underground was a no-brainer. This time, my journey starts in Norwich and ends in London. I'm meeting a friend in Heathrow (she's flying in on another airline), on May 16. We both arrive around 7am, but in different terminals. We need to get to Norwich, to meet up with 4 other people. The plan is to take the Heathrow Express to Paddington, then the underground to the Liverpool Station and then the train to Norwich. My question is, would it be to our advantage to purchase these tickets in advance? If we do buy the tickets in advance, if we miss a connection, will we be able to use these same tickets on a later train? I was thinking of booking the departure from the airport around 9am. Thanks in advance!

All you need to know about trains in the UK - https://www.seat61.com/train-travel-in-britain.htm

Another option is the tube to Kings Cross, and a change of trains at Ely. It takes longer but I think might be easier. (Note, you want Liverpool Street Station, not Liverpool.)

There is a direct National Express coach at 9:00, but I wouldn't count on getting through Heathrow in time. There are other coach options with one change at London Victoria.

Enjoy Norwich - I was there in 2018

If you buy your tickets ahead of time it is less money. Like thursdaysd stated Seat61.com is a good site.

No need to book in advance. Take the TFL train (called the Elizabeth line from about a week after your arrival.) to Paddington -- not the HEX. Takes maybe 10 mins longer for a fraction the cost and you can use the Oyster you likely still have from your last visit. Or if you don't already have Oysters you can buy from the machines at LHR. Then the tube on to Liverpool Street

(From May 24 when the Elizabeth Line is 'completely' open you could take it all the way from LHR to Liverpool Street but will still have to change at Paddington for the next several months)

Your biggest problem will be meeting your friend at LHR . . . with operational issues besetting arrivals, immigration, luggage, etc plus arriving on different airlines at different terminals meeting up may be the most complicated part of your whole trip. Make plas to meet at LHR -- but I'd definitely have a plan B ready in case one or more flights is delayed, cancelled, re-scheduled. It might be necessary to travel on to Norwich separately.

Didn't see Paqno's post -- TFL train tickets are not discounted by advance purchase. They are the same as zone 6 tube tix . . .

HEX tix are discounted when purchased in advance but they are too expensive to begin with, and even with a discount cost more than TFL.

The ticket to Norwich would be discounted.

Agreed, but to buy in advance w/ a discount (and it would be a pretty substantial discount) they'd need to pick a specific train from Liverpool Street, and arriving at LHR that would be difficult to do.

There is a substantial cost difference between Advance and walk up tickets on the Liverpool Street / Norwich route. I used to buy 2 sets of Advance tickets, departing 2 hours apart, in the hopes that I would make the first departure (and I usually did), but knowing that I had a backup plan if not. Even allowing for throwing away one set, it's still far, far cheaper than buying walk up Off Peak tickets, let alone Anytime ones.

Yup. I did mean Liverpool Street Station.

Thank you all for you input. I agree with janisj, that meeting up at Heathrow wiil be the most challenging. We're both leaving from O'Hare at the same time, but on different
airlines (why you ask...she's going on to Spain and Portugal after Norwich, so she booked her trip thru a travel agent), so we'll be able to check each other's departure times. After doing a bit more research and taking in all your advice, I think this route is the easiest, with only 1 transfer...Picadilly line to Holborn. Change to the Central line, taking that to the Liverpool Street Station.