I'm having my boiler put in the loft. The power to it at the moment comes from a single 1.5mm cable straight from a Wylex NN916 consumer unit on its own NB15 15A Type 2 breaker. When it is moved I would like to add some extra sockets - 1 for a whole house pump, 1 for an aerial booster and a couple for anything else, e.g. Sewing Machine, Computer etc. What is the best way of achieving this.
A you have a radial on a 15A mcb then there is no reason why you can't extend it to several sockets as long as you realise the limit of load, as boiler system usually only requires a 3A fuse, leaves nominal 12 A for other loads this equates to almost 3 kWatts so your proposal is reasonable although power circuits normally wired in 2.5mm as long as mcb not uprated no probs.
If boiler being moved it might be a good time to upgrade circuit to 2.5 on 20A mcb then as above but higher load now poss. ie blr, plus 4kW.