I don't know the limits off the top of my head, but I think the only problems they had with wings coming off were with the early Seafires, where the wings folded to fit on the carrier lifts.
I recall from Jeffrey Quill's autobiography that the structural failures which did occur were the result of C of G problems, which they cured by fitting bob weights to the elevators.
My uncle worked for Supermarine as an inspector and I remember him telling me about one of the later Spits (a Mark XIV I think) which they had back at Eastleigh for repair after it had tangled with an FW190.
The Spitfire pilot had got away by going into a steep dive followed by the 190. He managed to pull out at low level, but the 190 piled into the ground. When he got the Spitfire back to base, they found that the wing spars had been bent up about 10 degrees.
The aircraft was sent back to Supermarine for a thorough inspection and for a repair schedule to be formulated. It was eventually repaired and sent back to the squadron.
The spars on the Griffon Spits were solid rather than nested tubes, but it does show they were very strong indeed.
Re: the TV programme. I saw the second episode last night, and think it is getting better and better. As others have said, the veterans came across really well. Especially moving was Bob Doe saying how he had shot down a 109, but couldn't bring himself to finish off the obviously crippled aircraft. The pilot was subsequently rescued and went on to shoot down more RAF aircraft. What a dilemma to be faced with?!!
Looking forward to next Monday's episode.
RD
