Thanks Swarfy. The pump spins freely if I loosen the four screws on the end plate, but seizes up firmly when I tighten them again. I've read the threads on how to fix it, but replacement seems the safer bet. I will be ordering a new SRM oil pump as soon as I recover from the shock of the price.
On a B44 pump (similar) I found that a tiny bit of corrosion/swelling on the body, under the gears, caused exactly the symptoms you have described, to fix it I measured the width of the gears (the gears next to the plate, the drive end gears were not the cause) and then used wet and dry sandpaper on a piece of glass to slightly reduce the gear width, by under 002. This fixed it and saved a bundle of $$$ compared to buying a new one.
I have maybe 6 of these pumps, two I have fixed for spares the other 4, I am 99% certain would respond to the same sort of treatment.
To get the extra 35% flow of the srm pump you can just buy a65 gears and fit them in an A10 body, or get a whole a65 pump and fit the a10 drive end into it.
As you can tell I am too mean to buy the SRM pump!