buy a new flexi section, cut out the old and weld in the new only way really, or if its just to get through mot, smother it with exhaust putty so its sealed, wont last but it should get you through lol
Scrap the car but keep the damaged bit, mount it in a frame and sell it as "Art", then use the proceeds to purchase a Rolls Royce...........................................................
Or you could go to Callows in New Ferry, they repair exhausts or can even scratch build them.
Silver tape will secure it for an MOT - before the heat gets to it.
Failing that, you either need to relace the flexi by cutting / welding a new one in (new section will be about £15 plus fitting), or, replace the section of the exhaust - either new or find a good used one off a breaker.
I just bought middle section pipe for £22 from LVW on Cleverland Street, now comes the hard part, as I can not undo the 2 nuts on the join, as socket just keeps slipping, so I may have to get angle grinder out.