There are two regulations as to sockets heights the electrical regulations only say there should be room for the wire to leave the plug without harsh bending and Part M regulations covers new sockets in new build giving min and max heights for the disabled. This is normally 450 to 1200 mm from finished floor level but this is not hard and fast and for example you can still fit a socket into a power outlet in the floor as often found in open plan offices. It is also slightly different for public buildings and domestic. If you can show good reason why it should not be at the height most inspectors will still allow it for example matching all other sockets in the house or to avoid damage like behind a bed head.
The socket heights will not in the main effect the issue of a periodic inspection or installation certificate it could but could effect issue of a completion certificate.
There is a link in projects to Part P from that you should find Part M which is a free down load if you want to check for yourself.
thanks for your replies. I have now been told that the certificate can still be given if they are placed at 30cm from the floor!! I personally think that 45cm from the floor is too high and doesn't look right after viewing a new build for ideas. But I don't want to put it at 30 and then have to change it to 40 cm
For non domestic it is 400 not 450 for sockets I have never worked out why lower for non domestic. Much depends on building inspector in my mothers house quite a few are too low so she can reach in wheel chair.