Where (in the UK) can i source one of these estate boot lock covers? 

 

http://www.skodaczesci.pl/oferta/czesc.php?id=4288

 

 

 

Any skoda dealer spare part department, TPS if their local operation sells to public or scour ebay until one comes up from a wreckers. There is something on there at moment but it is a complete part of the rear boot sill trim including that bit.

As above. Quickest and easiest route is probably a dealer. I wouldn't expect that to be too expensive either. When I purchased my current Scout I noticed that bit missing. I pointed it out to the garage and they replaced it by the time I got the car a few days later. 

I cannot always get to a Skoda dealer spare parts department, hence online would have been a better option.

Online is handy for sure but I do order my parts/accessories over the phone. If you give them your vehicle reg. and describe what you're after they should be able to get the right thing. I'll have a look at mind and see if I can see a part number on it.