Is this day in London itinerary too crowded?

It will certainly fill the day, but it's doable. I doubt that you'll spend 2 1/2 hrs in the Abbey, but you can easily slide lunch and the war rooms earlier.

I think it is doable. If you do get done with Westminster early, lunch can be earlier or you could just wonder around near the abbey making your way to the War rooms. I think I did in one day Portobello road market, Kensington, went to King's Cross and went somewhere else.

Definitely doable. There’s a nice cafe at the Abbey or you could try a pub lunch. One of my favorite pubs the Two Chairman is less than a 10 minute stroll from the Abbey.

What are you doing at Parliament for 4 hours?

Sounds like a resounding “doable”! I’m trying to build in a lot of time for walking slower. If I’m able to do Westminster Abbey and the Churchill war rooms before lunch, maybe I’ll do Kensington Palace, Kew gardens, or the London transport museum since I’ll be on the London Pass that day.

Thank you for the pub recommendation!!! Google reviews rates the Churchill war rooms as having a good café too. Any thoughts on that one?

I most certainly do not expect to spend 4 hours at Parliament! :D The extra time is for travel in case I hit rush hour. I also want to stroll around Soho.

To me the cafe in the War Rooms is small and it's part-way thru the tour route so it might be OK if you need something to drink by the time you get there. I'd eat at the Cellarium Cafe at Westminster Abbey. I had delicious food there last year but I've vegan so take that in to consideration, lol!!

http://www.westminster-abbey.org/visit-us/food-and-drink

I can and have spent 2.5 hours in Westminster Abbey. Do download the free audio tour onto your smartphones before you leave home. I love the Verger tour which is 5£ more, I think, then you'll want to spend some time in the areas not covered by the tours.

To me your time in the War Rooms may be a little short but I also enjoy these a lot and perhaps spend more time there than most do.

I would not be able to do both Westminster Abbey and the War Rooms before lunch! I'd spend time at both those places before Kensington Palace.

If you haven't bought the London Pass (so that's why you actually are trying fit a gallon in a pint pot, because while what you suggest is doable but I will be the one to question the desirability) perhaps consider a touch if all this running around trying to make it pay is best for your vacation.

As of March 27 the ticket to the Churchill War Rooms are a timed entry.
https://www.maximweb.net/ImperialWarMuseums/day/?eventconfig=7&_ga=2.47326693.314715402.1521062748-1698276104.1519837737

You have lots of great advice here already.

You may want to do the Churchill War Rooms first, then move on to Westminster Abbey.
The reason being that the ceilings are very low in the Churchill War Rooms. Some of the rooms are small, the hallway connecting the rooms is narrow. The large room--museum--containing the Churchill memorabilia, clothing and photos is large but with a very low ceiling.
When the crowds move in mid-morning, it is elbow-to-elbow in some of the rooms and the hallway.
My advice is to be at the Churchill War Rooms when they open and get in and done before the crowds roll in.
As Pam said, there is nothing special about the lunchroom at CWR; pretty basic.

After the War Rooms, go to Westminster Abbey. Even if it is beginning to be crowded, the interior of this place is huge and can accommodate a lot of people. (Not so for the War Rooms.)
The lunchroom will be much better at Westminster Abbey than at CWR.
We had great sandwiches and salads there.
You may not be able to do both sights before lunch, but you can try, and have a late lunch.

I also love Claudia's suggestion of a pub lunch.

Thank you for all the great info!!! I definitely will either have lunch at the Cellarium Café or one of the recommended places. That’s a great idea doing the Churchill War Rooms first. I’ll probably do that since it’ll be less crowded and easier to determine what time to get my entry.
I have lots of time in London but since I’m planning on doing the following:
26 bus tour
21.5 tower of london
9.8 tower bridge
10 thames cruise
22 westminster abbey
18.9 churchill war rooms
18 st pauls
126.2 total where the 2 day pass is 94. I tend to want to go go go when I travel so I’m thinking I’ll do two site seeing filled days and then relax the next day. Even so, no, I haven’t bought the pass yet until I get my schedule a bit finalized and I’m sure I want to do it.
Y’all have given me some great advice so far! Want to take a look at my other days? Here is what I’m sketching out for my first London Pass day:
6:15 or so – Leave hotel to get on tube to Covent Garden before rush hour (should I do this? Would it really help?)
7:00 – Breakfast nearby
8:00 – First Double Decker Bus Tour
9:00 – Tower of London (jewels first then Beefeater tour)
11:30 – Lunch
12:30 – Tower Bridge Tour
14:00 – travel to St Paul’s
14:30 – St Paul’s (I’m climbing stairs and adding 2 flights every week in order to be able to make it to the top!)
16:00 – I could do the London Eye or Walk along the Thames or maybe a walking tour or maybe an early dinner
18:30 – Tube to Temple
19:00 – Hidden Pubs of Old London walk
Let me know what you think!!!!
My favorite part of past trips were meeting new friends and trying new and delicious food. So after these two days, I’ll see a few more sites but focus more on that.

Bill in AZ, thank you so much for that info. I had not seen the War Rooms have timed tickets now so I appreciate the head's up! I think I've always just walked up before.

You're welcome Pam.

You may want to secure reservations for Westminster Abby now. Based on a recommendation, I looked at their website and only one Day was available during our week long trip in late May. Just google their website.