Do I need to move electrical wiring if intending to improve loft insulation and boarding out loft?

BS7671:2008 requires that a correction factor is applied to allow for the additional heat that will be retained by the cable that can't be dissipated as easily. It would be extremely poor practice to have joints on the cables, so it would be best to completely rewire the circuit. You must apply to your local authority and pay to get part P building regulation consent before you start doing DIY electrical work, otherwise you may end up being fined £5000 for breaking the law.

If you intend to DIY follow the good advice given by ESS above with regard to notification etc. Might prove less costly to hire a registered competent person who can notify on your behalf for a lot less dosh. The technical electrical matters will need further research by yourself if you intend to DIY. Then again, hire a reg comp person who has the tech knowledge to do it for you. Depending upon the 'load' on the circuit it may be that no alteration is required. Could you determine that..? If in doubt (puts needle to old record) hire a....