London prepurchased tickets ? refunded??

Tower of London web site is quite clear: tickets may not be returned etc. You have tickets so either go or write it/them off as a loss. Sorry. I suspect your other tickets are equally Nonrefundable. But in light of the millions who are suffering, tickets are just a sigh and move on, nothing to fret or even think about.

I’d say wait and see for these small pound amounts.
The Tower of London is a sight that could reopen and attempt to maintain social distancing. Then again, it could be difficult trying to maintain distance inside the actual towers.

Same with the theatre. I don’t see a packed show happening but perhaps open with reduced numbers in the audience.

Contact the venues and ask. I read that some people with clearly marked non-refundable tickets for the Alhambra in Spain were refunded their money because the venue itself was closed. You have nothing to lose by asking since these are not normal circumstances.

Tower of London
https://www.hrp.org.uk/coronavirus-covid-19-statement/#gs.5zeald

Can I move my general admissions ticket?

If you have purchased your general admission tickets through Historic
Royal Palaces, we will happily alter the dates of your visit.

Further information

Your ticket will be valid for one year from the original intended
visit date. Please contact our Customer Services team by completing
the Contact Us form.

As you will appreciate, we are receiving high levels of enquiries at
present, so please bear with us as we work to support all of our
customers.

If you purchased your ticket through a third party, you will need to
contact them directly.

Can I get a refund?

You may choose to re-book for another time or to donate the cost of
your ticket to Historic Royal Palaces. As an independent, self-funded
charity, we rely on your support – which is more crucial now than
ever.

Here's an article I found on the theatre district. It appears that most theatres are offering exchanges, but to contact the box office based on circumstances. https://www.standard.co.uk/go/london/theatre/west-end-ticket-refunds-coronavirus-cancellation-a4388746.html

I was to be in London this month. This is what I got for things I purchased..

Ticket for Hamilton......received a credit for a ticket next year
Heathrow Express...received a credit for ticket next year
Train ticket..... received refund
Hotel in London....received refund
Hotel in Manchester.....received refund
Plane ticket....credit good for two years, will be using it next year

I was supposed to be in London this week and got refunds for my theater tickets because the shows were cancelled. One was issued automatically, the other I had to contact the theater box office to request a refund instead of a credit towards a future performance. London theaters are now closed through at least 28 June, so you should be able to get either a credit or refund for any theater tickets before then. You’ll want to check websites for every provider that you bought any kind of advance tickets with, they all have different cancellation policies right now and those policies continue to change as closure dates are extended further (which may mean you are better off waiting to cancel some things until closer to your trip dates).

One thing to note that seems to have surprised a lot of people is that exchange rates have changed rather dramatically recently. Unless you live in the U.K. and use Pounds as your local currency, the refund you get once it posts to your credit card may be lower than what you paid because your refund isn’t worth as much in U.S. dollars (or other currency) as it was when you made the purchase.