Yeah, just make sure you properly invoice your other services to the clients involved, declare the income to HMRC, pay tax & VAT on it, properly register your other business activities and have your administration in order... Simples!
The net is closing around the self-employed-but-working-for-one-client-only-construction, mostly for the social security contributions dodged by both parties involved. In Italy, France, Norway, Belgium and Germany there is increasing pressure on Ryanair to properly employ people. Question of time, I think.