sophie78: I need a £10k unsecured loan to refurb my house. I applied to the Abbey who turned me down.
These things seem to happen for no obvious reason, however you should ask for as much of an explanation as Abbey are prepared to give you. Seperately, if you bank with Abbey, you need to make them aware that you consider no explanation to be unacceptable customer service. If you don't bank with Abbey why are you applying to Abbey?
They must tell you which CRA they referred to. Whenever you get turned down its always worth checking your report (not your score) for problems (and to confirm that Abbey did actually search your file).
It's also possible that you have been declined on affordability grounds, either genuinely or by mistake. Other affordability issues can also include too much available credit. In that case you need to reduce credit limits to a level you actually need. It's also possible (you didn't say) that, while you have no defaults or missing payments, you are only making minimum payments on your cards. That is a big no no to further credit.
TBH, Abbey need to be "encouraged" to be more forthcoming.