Solved and sorted the issue of the gurgling sink basin, but i was still left with an inaccessible stop tap.
He gave reasons for why he didn't want to cut an access hole that sounded reasonable at the time, and gave advice to use the street cut off, but this isn't a proper solution.
He seemed to be under the weather and that advise benefitted him more than me.
Response from Mr Small Job Plumbing Ltd
I am sorry you felt dissatisfied. I was more than happy to cut out your unit and change your stop tap but was actually trying to save you money and at the time you where happy with the advice. It would have cost between £150 and £200 to do all the work needed to change your stop tap, but I showed you where you could get a outside shut off key and how to do it which takes as much time as it does to turn a stop tap of. The key would have cost you £15 so I was trying to save you quite a bit of money. If you wanted me to come back and change your stop tap I would have been happy to do so. Thanks