Since 14 April 2020, all credit cards have been banned from gambling in the UK. There are no bookmakers exempted from that rule. You can bet, however, with your Mastercard debit.
Usually, payouts reflect in your card within 3-5 business days. In some cases, it can take less, but most bookmakers provide the time frame above. The most significant factor is your bank, plus the amount you want to withdraw.
Yes, it’s one of the most legal payment methods, and bookies that accept it are trustworthy. It would help if you kept in mind that legality also depends on the legal framework of gambling in your country. Plus, if something goes wrong, you can ask for a chargeback from your bank.
If you deposit to Bet365 with Mastercard, the process is instant. Withdrawals though can take 3-5 business days. Also, both transactions are free of charge.
Straightforward answer, yes. You are able to use your Mastercard to deposit on Betfair. However, in some countries, if a player uses a Mastercard BusinessCard to deposit he may not be able to proceed with any withdrawals.