I wish to extend a ring main into a new conservatory.

I have a socket on the existing ring that I can extend from.
Obviously one end of the old ring and 1 new wire from the conservatory
will be connected into the original socket.
The other pair of wires thus need to be connected together to complete
the ring.
I know that ideally I would use a 30A junction box to connect them
together, but I don't have any spare cable on the old ring. Is it OK
to connect the wires inside the existing back box using choclate block
or is this a big No No?

If not what are my options?

Thanks

Paul.