Update: The problem has finally been solved!
Colin (and Louise) at Lincoln Sentry were really helpful in trying to work out my problem (initially by phone) and finally by Colin coming in to take a look at the problematic pantry. He fixed it with ease (apparently the frame had been moved too high somehow and just needed to be lowered slightly)... I'm sure many of you might have worked this out by yourselves, however for me it was totally unexpected (gravity pushes things down not up!) so I was really happy and relieved that now finally my pantry can close!
I'd like to thank all here that have tried to help me, I really appreciate the time you guys have spent trying to help troubleshoot my problem (despite my bad descriptions!).
I'd also like to thank Colin and Louise at Lincoln Sentry (they werent the only ones I tried to contact about my pantry however, they were the most friendly, courteous and helpful company I approached/ that bothered to reply me). In this "modern world" we live in, I find this type of professionalism rare (in any industry) and I want others to know of their efforts which they gave without trying to charge or sell me anything. In addition, they normally deal with builders etc so I was even more impressed that they bothered to help me (just a normal householder) at all, especially after some of the abrupt responses I received from another company who basically told me to find the cabinetmaker (which I would have IF I had known whom that was)!