I recently purchased a boardman road bike and after 5 weeks as soon as you put effort into peddaling I am getting a squeaking noise from the bottom bracket, I took it back to halfords and they said it needs greasing every so often, is this an easy job to do and should I be doing at after only 5 weeks
It should not require greasing after only 5 weeks, unless it was not done originally.
A noise of that type can be caused by basically 4 things in the Bottom Bracket:
Options 2 or 3 are likely given the fix described. Both would be repaired by removing, greasing and retorquing the BB.
The most likely cause after such a short time is that they were left loose or dry during assembly, and that the shop or mechanic was talking CYA.
But that is difficult to determine from several thousand miles away. You can be confident that the maintenance does not need to be performed every few weeks. Your twice yearly tune up should be enough.