It might vary depending on which bank you’re with. I tried looking it up for my bank. It doesn’t say there’s a limit on how many times you can use contactless consecutively. Most bank websites don’t say either
However, Barclaycard, says: “For UK transactions there is no daily limit on contactless payments, however there is a limit of £30 per transaction and you need to have enough money in your account to cover the cost of your purchase.”
TSB says: “You can use it as many times a day as you want, but every now and then you may be asked to enter your PIN. This is to double-check that it’s you who’s in possession of your card.”