I've seen proposals both ways. Some systems just say 'give everyone #1200 a month' or whatever, whereas some sa 'make sure everyone has 1200 a month at least to spend' - so the latter system is a top up system, not a blanket payment system.

The problem with a top up system is that its (almost) as complex and so costly to run as the current system

People will have to apply for the top up - those on irregular contracts will need to keep applying / cancelling their benefit on a good week. You will need to check for fraud, work on how you claw back monies owed etc etc

One of the big selling point so the universal benefit system is that it is very cheap to administer. Once someone is on the system they get the £xxxx until they die