Use ULTRASEAL and you don't get flats, the demo I saw had over thirty 5mm holes put in tyre and it lost less than 1 psi, I was there at the time and did the holes myself so there was no fiddling going on.
This stuff has all the approval marks for PERMANENT REPAIR, it is also used in places such as NI , so spike planks don't work.
I have had it in tyres for over 20,000 miles without a problem, until they are worn out.
A lot of bikers use it also, and has been tested at 256 MPH so a cossie will not worry it, I know of someone who wrote a piece on the stuff when they had it fitted in their BMW bike and went all over the desert, which is puncture city, no problems at all.
Ask yourself what you would rather do change a wheel on the M25 motorway in the pouring rain, whilst all the traffic goes past, carry on and possibly shred your tyre and have an accident anyway, but alt least cost you a tyre and time, or wait until a nice day and just pull out the screw or nail etc ?, easy choice for me you make your own mind up.
This stuff is considered a permanent repair by the standards people, I have had a tyre that had a 8mm bolt in it, pulled bolt out and did over 10,000 miles after.
As to get it fixed for £5 show me where, the one I had done for a freind was £16.87, which is half the price of a ULTRASEAL.
These quick fit places are full of crap advice as they push the industry to try and get ever tighter legislation passed so they sell more tyres.
THEY ARE CURRENTLY TRYING TO HAVE ALL PUNCTURE FIXES ILLEGAL, on any tyre for a road vehicle, not just high performance ones.
Repairs are so dangerous, ALL LARGE AIRCRAFT LAND ON REMOULDS, we ARE talking 747 etc here.
tabetha