........to a possible solution for all those with poppy off front bumpers
The problem with mine seems to be the metal strengthen strip on the bumper immediately below the headlight. It doen't appear to be the correct curve for the shape of the car - tis only very slightly out and not a tight enough curve, so this exerts a 'push' on the inside of the bumper in the vicinity of the side clip ergo popping it off due to normal road vibrations.
So the remedy (worked on mine, try on your's at your own peril :shock - remove the two top centre clips and the two screws in the offending side's wheel arch and pull the bumper out a wee bit on the offending side to gain enough room to work. Then slowly ease the metal section to a tighter curve. This took a bit of trial and error to get the correct shape, but keep refitting temporarily and you'll get a good snug fit. Go gentley and try not to crease the metal section. Once happy with the shape, refit the fixings.
My clips had been somewhat weakened by continual 'knee pushes', so I used a very small amout of clear silicon adhesive on the clip to give a bit more grip. Whilst this was drying I left the two top clips out and pulled the bumper forwards in the centre as far it it will go and left it to dry overnight.
This morning, I refitted the clips and have covered over 70 miles today on Derbyshires finest potholed/badly surfaced roads (inc several farm tracks) and it's still as it was this morning .