As per Paul's advice, the front bumper trims can be gently removed from the bumper. Don't try and go behind the bumper, you can't get access, so just work from the outside.
1st attempt (with local mixed paint and matt clear) didn't go well at all
The paint I had made was much lighter than the original and the matt clear ruined the lot!
Did some more research and found that even though I was told by my local main dealer that the paint and paint code was not available from Renault, I found the Renault part number for a 400ml can of spray! I went back to the same main dealer with the part number and they sold it to me for £7.43 + VAT.
So if anyone needs it:
Paint Code: 205139
Colour Name: Pierre a Fusil
Renault P/N (400ml aerosol): 77 11 238 903
2nd attempt with the Renault supplied spray was much better, but the colour is still slightly lighter than the original, so I will take the rest of the trim off the car and spray it as well.