Buying tickets ahead of time?

Repurchase? Do you mean pre purchase?

I’ve just returned from London. Very very crowded.

So YES would be smart to buy tickets in advance but don’t be surprised if tickets are unavailable.

Think the store you mentioned has closed.

When you say Westminster, you need to be specific. Westminster is a large part of London and is also used colloquially to mean the UK government and potentially the Houses of Parliament. There is also Westminster Cathedral.

I think you mean Westminster Abbey. I’m not trying to be pedantic here but even more than other places in London, it’s really important to be specific on this one.

It’s a good idea to pre-book tickets for Westminster Abbey but not essential.

For the others, there’s really no need. You might want to look at whether membership of Historic Royal Palaces is worthwhile - I bought this at the Tower of London ticket desk on the day of my visit, and it then enabled me to walk into Hampton Court Palace without queueing for a ticket.

Tower of London
https://www.hrp.org.uk/tower-of-london/visit/tickets-and-prices/#gs.6yemec

Westminster Abbey
https://tickets.westminster-abbey.org/

Hampton Court Palace
https://www.hrp.org.uk/hampton-court-palace/visit/tickets-and-prices/#gs.6yezs6

from their website:

The Gymshark flagship store will be located on Regent Street, London,
United Kingdom.

WHEN DOES THE GYMSHARK LONDON STORE OFFICIALLY OPEN? The 18,000sq ft
space is currently being renovated to deliver a truly amazing and
unique Gymshark experience for our community, and will be opening in
summer 2022.

Check back soon for more information on open dates.

It is summer 2022. No evidence yet.

The Westminster Abbey site linked above will tell you how many tickets are available for each date/time slot. The Tower of London site uses a red (sold out) - yellow (limited) - green (good availability) for dates/times. Both look like the am slots are starting to fill up for Monday-Wednesday next week. When we were in London in June, I checked the sites' ticket availability regularly before flying. I wanted to wait to book until we were in London in case of Covid/flight issues, unless things were absolutely selling out. That worked for us, but London may be more crowded next week due to school holidays.

Thank you all for your advice.

Well, the trip to London is cancelled. My daughter and family spent five hours on board the plane before the flight was completely cancelled. They had only five days in London, and at best it would be four and their flights were over $2,000 apiece. Travel this summer is horribly disappointing.

Oh dgawell, I'm so sorry to hear this! How disappointing for you and your family. I hope you are able to do something else that's enjoyable with these 5 days, and that you can visit London in the future.

Thats horrible. May I inquire which airline?

American Airlines. This all just sort of shows what a mess traveling this summer has been. We took TAP (Portugal) back from London in May and had a very efficient experience with them and at Heathrow.

Where were they flying from that they boarded and sat for 5 hours before cancelling?