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I have never looked at google.de before today so it may have swopped over from google.de to google.co.uk. Today its not in the top 200 for the internal german search and about 50 for the full web search.
If that is the case then getting UK links is the main reason you will show, along with the fact that your sites are .co.uk.
I would always recommend hosting in the UK for .co.uk domains, especially if your target is indeed the UK.
However, as you have made it whilst being hosted in Deutschland then I would not worry about moving, unless the service is poor.
If you could do with better service then I suggest you ask Rackspace for a quote if you are serious about service, upteime and server speed. (I'm not allied to them in any way).
Good web hosting is very much like a like a luxury car, you don't realise how much better it is than a 'standard' car until you have tried it. If you can afford a decent host in the UK then go for it, you will not regret it.