When flying internationally, we have gone through immigration at the regional airport many times. Probably will not work if flying a low cost, but should be OK with Thai or Bangkok Airways. Then you would get yr stamp in CM.

Normally a current account is the account that a cheque book and debit cards are issued against, your salary/pension or whatever income you might have will be paid into, and any direct debits/standing orders will be set up against. In the "old days", a current account paid no interest and a savings account paid interest, although these days that distinction has blurred a bit.

We used a current account statement, but they only seemed to glance at the bottom line. Would perhaps only be a problem if the ISA is locked in for x years.

You would have to start the whole process from scratch again.