imperial stop cock

As the weather is no longer so cold I wanted to turn on the outside tap again which I had isolated in November by turning off its internal stopcock. That stopcock is stuck shut. It sits in the a (former)c fitted with compression fittings on an old copper pipe which I believe is of half-inch...

I had to switch of the mains water and after switch on got low pressure. After the basic checks of running water through all the taps and all apliances no improvement. so I guess the fault is the stop cock and need replacing and there is there is the problem. The house was built in 1971 and the...