JMS writes:

I was informed of a new Co-op Credit card today - 12.9% APR - no
charges for cash withdrawals - or for cheques.

Borrow half your limit in cash over the month - taking it out of ATMs
- or use a cheque to pay off outstanding debt on other credit card.

When you get the bill - withdraw the other half of your limit to pay
off the "loan".

This show could run and run - a permanent loan at no cost.

It would only work until they either lowered your limit or started
charging interest on cash withdrawals immediately[1] rather than there
being no interest if you pay off each month.

[1] Are you sure that they do not already do this?