You're in luck that you're in the UK where I'd guess there's a much better chance of finding bike mechanics who still do frame work. I'm not in Bristol or the UK, but have heard many good things about Argos (don't know if they are the best choice for this job, but that's where I'd start). Around here, finding any shop with both the Italian tap and the skill to use it is a very long shot...I'd strongly recommend using the VO unit IF you can ascertain that it will fit within your BB shell and one of their units mates up with a crank you want to use. Even with shipping to UK I'm sure it's cheaper than re-threading to Italian.