6mm cable encased within an insulated wall is rate 32A.10mm cable is rated 43A.if a 6mm cable is run on the outside of wall exposed then it is said to be rated 46A.10mm is rated 63A.if you are correct with the figure you gave then you are at the top end of the insulatedwall rating so safety would say run 10mm cable or two seperate 6mm.30A breaker will need to be uprated if you fit 10mm cable back to your consumer unit or a new 6mm circuit put in
ck
February 2008