Electrician is putting to new sockets in, existing sockets are 45cm high, should I put new same height or lower down?

Like the answers above suggest there are national standards and locations to put electrical hardware - sockets and so on. Part of this is so that if you sell your house, or have someone living in your house who are disabled, old or whatever they are able to access the switches and sockets. Put a socket too high and someone in a wheelchair might not be able to reach them for example.

If it was me I would gor for the same height as the others to keep things consistent within the house

There is no National Electrical Code (NEC) specification of the height of wall-mounted electrical receptacles in homes. 45cmm (17 inches) to the top of the outlet is pretty much standard. I am an electrician and I always put them at 17 inches unless the homeowner request a different height. Now, some states do have a rule on this. California requires a minimum of 15 inches to the bottom of the outlet box. If you change the height you will end up having to repair the hole left in the wall. You are just replacing existing outlets so put them back exactly like they are.

If the wiring comes up from below you can lower them if you must. If the wire enters from above it will be too short and would have to be replaced from one location to the other. Absolutely No Splices in the Wall. (If he is a real live honest to goodness electrician he will know this and not do it.) And as Clay said, some states (and counties) Do have their own rules.

The NEC is actually only a set of Minimum Standards for the industry. It sometimes takes years for a local area to adopt the NEC at all, and it is not uncommon for them to be enforcing code that is several years old.

using the existing height for the boxes does make it easier to pull new wire if that is needed === if you want to change the height in a certain area then you should talk that over with the electrician [[[ make a list of changes and give it to him and then Pease get out of his way and let him do his job ]]]

Depending on the rules where you live put them at a height to suit you

The socket height is regulated by building codes.

Put them where they can be accessed the easiest.

the same