My trike has been outside all winter since I lost the garage. It's been stood for about 3 months and the brake master cylinder has siezed. There was a line of rust round the bit that the push rod pushes, so I soaked it in plus gas and tapped it in with a hammer and drift. It went in easily enough but has stayed in, locking the brakes on.

How do I go about freeing it off? Or should I just get a new one?

Assuming its steel, put in the electrolysis bath to free it off. Then a new seal kit should do it.

Don't take chances with brakes! Fit a new one

I've just looked on eBay and a new one can be had for £20. I've ordered one. Thanks for the advice.