...for a training fix (under the supervision of my flying instructor)!
After carefully listening out, I made my call to London Centre which was answered promptly by a very friendly voice who approved my practice pan and asked me to continue when ready. I requested a training fix and the controller simply requested my present heading and level and very quickly provided a fix of our position. At no time did I feel like I was 'being a nuisance', like on some frequencies! It's reassuring to know that those guys are there, should you ever need them.
So, apologies to any airliners over the south west of England this afternoon at about 16:00 local who also heard the call!
And thanks to the controller who fixed our position - I found the experience very worthwhile and I wouldn't be afraid to call in the future if I needed help for real!