Peter,
Re; classicswede's post above.
New calipers are only £45/side, which is a bit cheaper than I had expected. If you can fix the problem for £100 (with a bit of DOT4) in an hour or two then that would be a really sensible way to go. Take note of what Bugjam says about getting the hard brake line off, otherwise you will end up changing that as well.
For comparison: A rebuild kit like this one (just an example, it may not fit your brakes):
https://www.ebay.co.uk/itm/283677957...3ABFBMtKSsuLRg
... is only £16 (against £90) plus another tenner's worth of DOT4. I have used this type of kit many times and as long as the old item isn't too corroded they work pretty well and should fix the problem. It will take you at least a day (maybe 2 of they are badly seized) to get the callipers apart, rebuilt and back on the motor car.
Your decision: it depends whether you value your time more than the £75 difference in price.
Good fortune,
Alan