Which online tickets to purchase?

We were in London last Summer and didn't book St. Paul's, just showed up, no problem.
For Westminister Abbey, we had to book that, we did that the day before we saw the Abbey. The site is easy to find on the internet.

Tower of London, I had seen before, so we didn't do that, but I am sure you need to book in advance.
Churchills War Rooms, have not done that, but I expect you need to book ASAP.

One thing, we didn't want to take the Underground, so we booked one of the HoHo busses. We booked a Thames River cruise as well. River cruise was nice, from near the Tower to Westminister. One thing, the HoHo busses move slowly, we spent over three hours in the day we did the cruise and St. Paul's.

Any time you are looking to buy tickets, go to the official websites for each place. Don't use 3rd party sites unless absolutely necessary. Because you are going at a busy time of year, advance ticket purchases are important to have. All of the places you have named have audioguides. Westminster Abbey also offers a Vergers tour; see the website for info. The Tower of London has the Yeoman Warder tours which are included in the ticket price.

Restating the excellent advice to use only the official websites to book. No need to use third parties. I would book the War Rooms ASAP. They do sell out and even if they can get you in right away, they seem to pride themselves in making you wait if you didn't book ahead. FWIW, I will be in London the last week of May. I have already booked Westminster Abbey (including the Diamond Jubilee Galleries), St. Paul's, the Battle of Britain Bunker (in Uxbridge), London Walks "The Blitz" tour, and the Heathrow Express (to get to my hotel on arrival). All were booked direct. I likely didn't have to book St. Paul's or the Heathrow Express so early, but that's just how I roll.

If there are sights you would like to see on a certain day and time, it is always best to book in advance.

I visited all those sights--Westminster Abbey, Tower of London, Churchills war rooms, St Paul’s cathedral—in Oct. 2024 and booked them all in advance. Book the first timeslot of the day to avoid crowds.

If you have the Rick Steves England or London guidebook, they always provide the web addresses to the official websites for purchasing tickets. There are so many fraudulent websites now you do want to be careful and make sure you are on the correct ones.

We were in London exactly 2 years ago (April 2024) and went to several of the sights you mention. As suggested above, go to the sight’s Website, not any 3rd party tour company.

Westminster Abbey - we stood in a long line outside with everyone else who didn’t pre-book their ticket, eventually working our way to the main entrance. It was very crowded once we got inside. I saw several people show up with a printout in their hands who were let in a separate door as soon as they arrived. I asked, and they had a reserved time, which I presume had been booked Online.

Tower of London - we walked right up to the entrance, no reservation, no people in front of us, no waiting. Approaching the entrance, we passed through very long barricaded lanes that were set up for keeping people in line, so it would seem that there are days when there’s a mob waiting in those lanes. Many years earlier, on what turned out to be a Bank Holiday weekend, we stood in a long, slow line along what used to be the moat. Seems to depend on what day you’re there, but a reservation would remove doubt. The latest Yeoman Warder (Beefeater) tour had just started a minute before we got in, and we joined it in progress. Once that introductory tour ends, you’re turned loose to explore the grounds, the Crown Jewels exhibit, and inside the White Tower.

St. Paul’s - there was a fairly short regular line. We had an express lane, because we had a 10-day London Pass (affordable if you buy a Pass for lots of days and/or are seeing a ton of sights in a short time, but not cheap if you’re not in London for less that 5 days and/or are taking longer to see each sight), and got in immediately. As I mentioned above, having the London Pass didn’t get us into Westminster Abbey any earlier; we still had to get into the regular line.

Churchill War Rooms - we saw them years ago, just after they’d first become a sight, and got tickets at the door, no line, no wait. Nowadays, Online might be your only option. The Rick Steves guidebook provided us an explanation of the relatively compact sight, and no tour was offered back then. At the back of the War Rooms is a museum on Winston Churchill himself (included), which can take quite some time to see, if you linger.

I now see that PharmerPhil mentions the Heathrow Express (HEx) train, which zips you from Heathrow Airport to Paddington Station in western London in just 15 minutes. The earlier you book your tickets, the cheaper the train, so there’s a pricing benefit for booking Online ASAP.

Thank you all. One more question: is the abbey unlocked tour the same as the verger tour? If not, do you prefer one over the other?

We’ve never done the Verger tour, and I’ve not heard of the Unlocked tour. Are they at different times of the day?

While we were there, they did a mini-tour, more like a talk, of the Choir section. The audio guide, which was included in the admission, was cumbersome. Move was set to Japanese when I was given the supposedly English device, so I had to go back and get that fixed. The earphones weren’t fabulous, and it was sort-of bothersome to use while making way through the crowds.

The Jubilee Gallery, in the “attic” of the Abbey, was worthwhile. A small additional fee to get in, payable once you’re there (no need to book Online), with views down into the abbey, and artifacts that had been locked away for centuries, but now can be seen only if you’re in that Gallery.

is the abbey unlocked tour the same as the verger tour?

Nope, these are two different tours. I took the abbey unlocked tour this past Nov. and it was great. It starts before the abbey opens to the public, so is a great way to see the abbey and take pictures without the crowds. So, I highly recommend this one if you can get tickets.

https://www.westminster-abbey.org/abbey-events/special-tours-and-events/2024/august/abbey-unlocked-tour-august

They will open up more dates in the future.

Did you have to email them to get the tickets for the unlocked tour?

No, when you go to book, that tour will be one of your booking options:

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

So, you can book online.

Ok thanks for all the info!