Hi and welcome from Warwickshire.
I had my roof motor moved at Tony's place last year. There are some places that remove the entire roof to access the roof motor down behind the rear panel. However, it can be done by someone who is willing to climb into the boot and in a rather contorted position reach over the inside panel and work blind. Being left handed also helps.
I too recall someone from down the south east but can't remember where I saw that post. Prices vary - We got a bulk rate but anywhere between £120-£200 is good value. The cost to remove the whole roof is in excess of £600.
The motors tend to fail due to water causing corrosion - this can be rectified and the motor bought back to life with a little attention. Paying for a replacement is generally not needed. The other common mode of failure is the loss of fluid over time. Simply needs a top-up. If you can hear the motor running, this is likely to be the cause.
Good luck with the fix.
BTW - I'll be the first to ask - photos of your car are mandatory

We all love seeing photos of all the cars, irrespective of sate of health and condition.