Update: got the crank bolts off using a 15mm box spanner. Had to buy a set of them for a tenner to get the correct size, but I'm sure they'll come in useful for something. If only to fit the crank bolts back on.
Then I took the whole thing down to Corley cycles in MK where their kindly mechanic pulled the cranks for me. There was a funny moment when we were comparing our pulling tools over the counter. My pushing pin was smaller than his. Fnarr.
He did it completely FOC. So I'll probably be back there again soon for something else.
Here's a pic of the TA crank after a go over with bar keepers friend.
