Time to pay arrangements

In view of HMRC hardening attitude to time to pay, has anybody's client 'forced' HMRC into a TTP arrangement?

Have a client who got into arrears with PAYE, (not for the 1st time) but at present is up to date with current PAYE doesn't owe any corp tax or VAT and is sending HMRC payments on a regular basis to clear the arrears. They have refused him a time to pay arrangement, but my thoughts are what can they do? can't see they have much of a basis to take action against him. Has anybody had clients in a similar situation?, if so what was the end result?