The first thing to do is discuss with your chosen electrician where about on the kitchen plan you want your sockets and any switched spurs to be placed.
Your electrician will then tell you whatever what you want is within the current regulations and for anything that is not an alternative can be suggested.
By law all electrical work has to be done by a competent electrician. Amongst other qualifications in the UK the electrician needs to be Part P compliant. Part P is a government building regulation rule covering domestic installation. When all electrical work is finished they will give a certificate to the house owner stating that all alterations that have been done are incompatible to all the current regulations.
When the electrician is laying all of the cables in place, with the old kitchen removed, any cables going vertically up to sockets above the worktop can be left in a long loop and return back down to keep the ring main unbroken. Then the cable is run horizontally along the wall, just above the floor, until it is below the next socket where the cable can then vertically back up the wall and again, left in a long loop and returned back down. This continues up to any socket above the worktops until the ring main is finished
These loops are temporarily clipped to the wall while the kitchen base units and any tall housing units are fitted. Once all of the units are leveled in and fixed back to the wall the final positioning of all of the socket back boxes can be worked out. When the worktops have been cut into place but not joined together the socket positions can finally be worked out.
Tip if you have some spare worktop or a length of wood the same thickness as a worktop this can be placed on top of the base units to aid the marking out so that the socket back boxes are cut out and fitted before the main worktop is fitted .
It is a good idea to know what tiles will be used or at least the height so that a full tile or two, depending on the height of the tile, passes beneeth the socket back boxes. If the tiles are 100m / m high then two tiles high is best but if the tiles are 150m / m high then one tile high is ok.
Next make sure the socket comes on a vertical joint so that when the tiling is being done only a corner is taken out of each of these tiles.
To get the vertical joint positions work out which end of the wall you will start tiling from and take the width of a tile plus one grout thickness and using multiples of that measurement measurement mark on the wall the closest joint to where you want the socket.
This means that when the tiles are fixed only the corners need to be cut out to fit around the metal box.
Now draw an extremely accurate, level line everywhere there is a socket. The socket has around a 5m / m cover over the size of the metal box so the tiles need to be cut fairly accurately.
Once all the back boxes are fitted if the wall is solid the wires will need to be chased down the wall to below the worktop and then put into conduit before the chases or channels in the wall are filled.