Train travel from London to Harwich to board a cruise ship
 

We're flying from US to Heathrow, and have to get to Harwich for the cruise ship early Sept. The cruise train is booked. We want to take the train on our own, from LondonLiverpool Street Station to Harwich. We have hotel reservations in Harwich area the night before the cruise and we thought that we'd do a bit of sightseeing in Harwich. We'd like to take the 11:18 train from LST, but, of course, we can take a later train if necessary. Do we need to purchase train tickets before we leave the US, or can we just walk up and and plan on getting seats?
Also, how much time do we allow for the taxi ride from Paddington Station to London Liverpool Station. Thanks, REW2

Why do you want Paddington - and a taxi?

It would be cheaper and much easier to use a pre-booked car service all the way from LHR to Liverpool Street. The Heathrow Express plus a taxi will cost nearly twice as much and involve luggage schlepping at LHR and at Paddington.

I'd book a train from 3.5 or 4 hours after your arrival at LHR just to be safe.

We're actually arriving at Heathrow on Aug. 31 and staying at a hotel at the airport that night.. That gives us the full day before the cruise to get to Harwich.. Our cruise leaves on Sept. 2 from Harwich. Thanks for the info. I will look into prebooking a car service. (Where do I look?) Also, what about getting tickets before leaving US for the train to Harwich? Thanks again. REW2

I can only guess that you are arriving Heathrow very late at night causing you to spend the night there rather than in London. Sounds like you will have full morning and part of an afternoon to explore London before your train ride to Harwick.

Yes, late night arrival. We've visited London /UK before and thought that we'd like a small town experience. Plus, there's always the possibilities of flts. delayed or cancelled. That's why we're going in ahead of time. There are 2 of us.
Do we need to purchase train tickets to Harwich before we leave the US?

I'm not sure where I found this- Is UK gtc a reputable company for ground transport?Thanks for any help you can give us. REW2

You shouldn't need to pre-book train tickets.

A car service I learned about here on Fodors and used many times in the year we lived in London last year is www.justairports.com. Nice cars, nice drivers, you can book on line. Just be clear you would like to be picked up at your hotel the next morning rather than the airport itself that night. There is a place in the online booking form for comments or you can simply respond with more information when you receive your confirming email back.

Thanks for the info. I'll check it out. REW2