Under Ofcom´s General Conditions of Entitlement all network operators are obliged to provide you with a PAC code upon request. The only issue here is that you have not completed the minimum obligations of your contract which may make your existing network operator unwilling to port your phone number over to another contract.
Requesting a PAC code is usually interpreted by network operators as a desire to terminate your current contract. As your contract is still well within its minimum term there may be severe financial repercussions for doing this. As well as being expected to pay the remainder of your monthly payments your network operator may impose a termination fee for ending the contract early.
Networks may try and refuse to issue a number transfer from a phone that is still within its obligatory contractual period. However, once you have entered into a phone contract with a network, ownership of the corresponding phone number passes to you and so they have no legal right to refuse your request.
When requesting a PAC code you are not obliged to inform your network of the reasons you desire it, or where you may be moving your phone number to. The only issue you may wish to consider is the financial penalties for terminating your contract early. Your existing network is obliged to provide the PAC code within 2 hours of your request.