Electrical question....

[Lookrider]

I may of misunderstood what you were saying. You appeared to be suggesting that OP strips 3” of insulation off the cable to the hob and twist the conductors of the new twin and earth cable (these conductors will be solid not stranded) to the existing cables and tape the cables together!

I don’t believe that @Fab Foodie is stupid enough to do that and I would be insulting him by suggesting he might think about it.

If I have misunderstood then I apologise. If I haven’t misunderstood then I suggest you delete it.

No need for apologies ..probly my grammar

But just to help
The cooker cable is existing and will be used for a draw string ONLY

Tape 2 T&E cables staggered but neatly along a REPLACEMEMT cooker cable tape ends to form a smooth "ramp "

So that the existing cooker cable can effectively be used as a draw string the 3 solid cable be twisted together fir 3 or 4 "so as it does not come loose
Tape up this joint to remove any edges

Pull the existing cooker cable through toward the consumer unit and away from the concrete floor in kitchen

You will now have another cable for the cooker AND two T&E to join on to the ring main at the nearest accessible socket with tbe other 2 ends providing fir the new kitchen socket

The only bug bear being if tbe joists are tight holes and don't allow the 3 cables through ?
But if that's the case just pull it back and your back to square one

 

[Lookrider]

Maybe a picture helps

 

[Sallar55]

Fist up is the cable 6mm or 10mm T&E and that would be impossible to add two 2.5 mm T&E cables for the ring main using the domestic conduit sizes. Conduit would need to be massive, as any bend reduces capacity. As an ex spark if you want a decent job the only way is rip up floor and bury a 50 by 50mm plastic trunking or a large pvc bath waste pipe to island. That would put the build back and builders don't like setbacks as time costs money that needs to be passed on.

 

[newts]

I've been in a few houses on this site & AFAIK the cable will likely be in a small pvc conduit set in concrete on the ground floor.