dink12:
NO NO NO.
Any interest earned (peanuts) is dwarfed by the possibility of massive charges if you run too close to zero.
I take it you are saying you pay in £650/month and have outgoings of £650/month. ie you start and end with a £200 balance?
Some accounts, usually those with benefits of debatable value, do impose a minimum funding requirementt but not all.
Move if you are not happy with the Halifax service, otherwise stay.
Separately make sure your ISA is getting a reasonable rate.