In reply to gethin_allen and Thread:
after emailing the company that advertise for £20, and getting no reply, I thought I'd try a local, on my way to work, bike shop.
They wanted £20 to look at it, and couldn't give me a ball park figure, and earliest date was 16th March!!
So I eventually found a web site that sold the reamer / threader on line, but because of fookin Brexit are no longer delivering to the UK
Much searching again and I found a web site that looked English and ordered the reamer, tried to get the inserts on the same site, but they wanted £40 I think this was for 10 but it didn't say, of course I only need one!
https://www.deporvillage.net/unior-right-pedal-reamer-and-tap-58x24
https://www.deporvillage.net/unior-left-pedal-thread-insert-916x20
When I paid for it, expecting UK and courier service I thought it would be here in a few days (I didn't check, I know!!).
Turns out these are a Spanish company, and delivery is round about 10 days
Round in circles again to find the insert, which I'd found the day before on the office computer and I'm WFH now for another week!
Eventually found them below!! Bit was £4.99 and postage £3.50
https://www.sjscycles.co.uk/tools/var-pe04703-helicoil-bush-for-pedals-58-x...
So all in all I've now spent nearly £50 and still need to do work and wait!!
Anyhow, if anyone need their right crank reaming, I know bloke who might be able to help you out, soon.
Thanks for the replies, I'll let you know how it goes.