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If it was the same locations I'd say do it yourself (until I get told it's illegal by diable). We moved one light switch with an angle grinder (there were two nearby and wonky switches so we rerouted one of them and dug a channel for the wire to the other) and enlarged a load of single sockets into doubles with a chisel and a lot of swearing. Parts from screwfix. The only hitch has been that our walls aren't perfectly flat so we needed to fill in a bit with some caulky stuff. Cost us maybe 50 quid in parts and materials and took two afternoons.
CYOA-
Extending a circuit doesn't require notification unless it's in a Bathroom. Adding and changing sockets on an existing circuit are considered minor works for most locations. However, you are obliged to meet the standards for electrical safety which can be achieved by following the standard BS7671.
This would oblige you to check circuit continuity, resistance, insulation resistance and prospective fault current for the circuit and assess that the breaker meets current regs and would operate in fault conditions.
If the shit hit the fan in the future and someone died or there's a house fire a professional would face jail time if he hadn't done this, a homeowner could only be fined up to £5000.
A new amendment to regulations has allowed third party certification of electrical installation. So you can now find a professional who will test and sign off your work, it's not yet been fully accepted by the most popular certification body but they look like they will be allowing their members to do it soon. You are also obliged to engage them before you carry out the work.
As a householder you needn't worry too much about the law, you should be more concerned with the safety of the installation and if you feel that you have made a good job of the work and given consideration to the potential for short circuit/earth fault and danger to occupants in the case of a fault then you've probably fulfilled your obligation to health and safety. Being able to carry out the tests confirms to professionals who have a greater legal responsibility that their circuits are safe.
Airhead
We had 2 days work from an electrician, he cut 4 new sockets into downstairs concrete wall, tidied up, checked the wiring, rewired some stuff, changed 10 light socket plates, put swapped 2 singles for doubles upstairs. Cut in two into concrete, one into plaster.
540 with materials we selected from screwfix.
Would and have recommended him again.