Tenants Want to Leave Early

Other

More information would be great, were the tenants on an existing AST that could have rolled over to a periodic or were changes introduced to warrant a new AST?

Are you trying to achieve a seamless changeover without loss of money? Did you actually outlay money prior to them signing new AST or were you grateful they stayed so you didn't have to re advertise.

If they were good tenants why punish them for the change of circumstances, if it equates to something like lower/loss of income it could be cheaper to let them go and be thankful it hasn't gotten to an s8 notice where you could be outlaying more then advertising cost. If you use online moneyclaim, they could counterclaim as to how fair and your reasonable action is, so you would need to show proof re costs. An AST barely worth the paper printed on when Judges so fickle, technically you might be right but that won't always win the case - lots of sad true stories on landlord zone where judgment gone against LL .

I've had an hellish experience with a scumlife tenant, our costs went into thousands to get possession and property back into a rentable condition, I view writing off £500 as a lucky escape.

Consider seriously if it is worth pursuing tenant financially. It is difficult visualising you as a fair and reasonable landlord something more like opportunistic money grabber comes to mind.

This just my advice, I don't have all the information to hand so made an assessment from information given.