how do l replace my peugeot 206 petrol cap for a new one? the standard one has an inbuilt lock!?

the only way... braking the cap

start drilling the lock first, maybe you can release the lock and you can take out the cap

or. with a large pliers start braking the cap, piece by piece

Hi, it is unclear what u r trying to do, possibilities including:
1) u have lost the fuel cap key & can not open it
2) u have lost the fuel cap
3) u want to put on an aftermarket fuel cap

for 1), ask ur local locksmith if they can get the cap off & make a new key, or contact ur peugeot dealer with ur chassis number & ask if they can get u a replacement fuel cap key (or proceed with the other advice to break it out & then fit a second hand one - u may want to think about where u do this - crouched in a dark alley hiding behind the car, seems like a good way to get a visit from the local police!)

for 2), try to find a second hand fuel cap & key or purchase a new one (ouch?) (note that the cheap plastic push in caps that u can buy do not pass the vehicle inspection where l am).

for 3), ask at the parts store for one that fits ur car, if they do not have one listed for ur specific car, try ones that r specified for other Peugeots or Citroens