Any broker will be able to buy/sell these instruments on a clients behalf, whether or not they will is another matter. And I would be very surprised if they were able to offer you any advice on these things. Main problem is that the UK doesn't have well developed market at the retail level, historically we've had an equity culture.
Also bear in mind that some of this stuff ("distressed debt" is the polite euphamism for it) is not gonna have a vanilla structure and that your broker is NOT going to be able to rely on Bloomberg to accurately describe let alone model this (eg amortising fixed/float FRN's)