Hi pattis.
10 down. In word play . . .
provided = if
and contracted = n (informal shortened version, as in rock 'n roll.)
companion formerly = fere
Reverse the first two parts inside the third to give FENFIRE.
Def = burning natural gas.
11 down.
The extra word is:business.
In word play . . .
charge = fee
ultimately per = r (last letter of per)
Put the first round the second and add . . .
head = ness
Def = licence.
In the puzzle there are three extra words that have an I in them.