Sapose you save drive before long PNG, you may like to get some refresher lessons, but most important is to familarise yourself with traffic regulations etc for this country by going through the DVLA driving hand-books. There are some impatient & arrogant drivers out there on the UK roads, but mostly UK road users are the most considerate. If you feel confident enough to use your PNG licence like our wantok suggested, you may do so! I drove in PNG but still needed to do the refresher courses for my UK license. My advice would be for u to get some refresher courses. Although it can get costly, it's worth it. There are 2 parts to the theory test now both computerized 1. Hazard Perception is where u identify an hazand and click at the right moment to score points 2. Theory test, is a series of multiple choice questions. The best way for you to ready for that is to buy or borrow the theory test preparation books and try to answer as many of the questions as possible. trying to read every chapter is a waste of time, as it's too big a book. The final part is the practical tests. Your driving instructor should advise you, if you are ready for your practical test. It depends on your instructor, if u are lucky you may get a good instructor the 1st time. I suggest you be happy with your instructor, if not, it's your money, you can change. Without being descriminating, the youngish sort of instructors (about 40's-50's) are usually good.
Hope this is of some help! For more info look up the DVLA website.