This is a good question. The quick answer is no, matched betting won’t affect your credit file. However, if you go to try and get a mortgage or a loan and they ask for three months’ bank statements, you don’t want to hand them statements with hundreds of betting account transactions. They will look at this pretty suspiciously, as heavy gamblers don’t make for good repayers.
There is an easy fix for this. There are some great online banks now you can make an account pretty quickly, for example, Monzo and Revolut. Instead of using your main bank account to deposit and withdraw to the betting sites, simply transfer money to the new account (most are instant) and use it for all deposits and withdrawals. Then your main bank account statements will be clear of anything that could worry a lender.