I take it the bit behind your oven is a plate that looks like this: (but with a cable coming out of the bottom
If so then you can replace it with a single socket front, witch will allow you to plug your new oven in. You will still have your CCU above the worktop to switch off / isolate the oven..
Are you confident to attempt this yourself?
If so, SWITCH OFF THE ELECTRICITY. remove the front off the cooker outlet, remove the thick cable that went to the old cooker, remove the back part of the cooker outlet to leave a box with just a cable in it.
You need to make sure the earth wire of the cable is covered with earth sleeving, and that there is an earth wire connected to the earth terminal in the steel back box (this should have been connected to the old outlet)
Take your new socket and connect the live, neutral and the two earths (one from the cable and one from the back box). Make sure all the connections are tight, and the wires will not pull out. Screw the new socket to the backbox. Turn back on the power.
You should use a decent quality socket suck as MK or Crabtree.