Does anyone know of a device that will allow me to use VOIP from my place abroad to home (in the UK) and will then allow me to 'break-out' onto the UK PSTN?

In other words, I want to call from abroad but make UK-UK call.

Obviously almost any voip service will let you call UK PSTN numbers for a price, sometimes for free. If you sign up to a UK specific voip service such as Sipgate and your software or voip hardware device is setup to register to the UK sipgate server then as far as they are concerned you will be making voip to PSTN calls originating in the UK and will be charged their UK to UK rates (price dependent on what package you are signed to, either Pay as you go or the Sipgate 1000 package).This would also give you a UK PSTN number that UK residents could call at standard UK rates. This would also apply to any other UK registered voip service.