A little surprised today to find that a request for 6mm heat resistant flex at a branch of a chain of electrical wholesalers was met with "never stocked it" and a similar response to 4mm. They called another branch and the response was "use twin & earth". Without reference to regs I would have thought "if you can move it without disconnecting it use flex". You could (still can? ) use pvc flex for cooking appliances where not in contact with hot parts - so for a free standing cooker you could possibly be satisfied that the flex "run" was OK how can you do that for built in appliances?
Just for ease of installation as in getting the double oven into (and out?) of the housing I'll use flex but is cable allowable? - and how do you get the oven in without the cable "folding up" behind the appliance?
PeterK