If you are doing it with a school then they will have gear you can borrow for the time you are doing your training and test. You will need to show the examiner that you can safely ride the bike on NSL roads so yes he/she will take you onto a dual carriage way ( dual carriageways have a speed limit of up to 70 mph) and he/ she will expect you to ride at those speeds if safe to do so. The examiner will give consideration as to the bike as well. If you do the test on a 125 he/she will be aware that a lot of 125's will struggle to hit 60, let alone do 70. Note if safe to do so, that will depend on a variety of factors such as traffic, condition of the road, weather etc. As to being skint and not able to afford the gear look on eBay et al,as quite often there is second had gear available.