That's a standard 5 pin relay and was fitted to thousands of different model cars since the 1950's. It's available over the counter at any auto accessory shop.
Don't go looking for the exact part number when looking for relays or other electrical items unless they only came on your car otherwise it gets expensive.
Love how the Polo has turned out, well done!
I belive I have the same problem with mine ( I haven't driven it since 2007 mind), but do you have picture of the other side with partnumber or can tell me what kind of relay it its?