To get a closer look at the reptiles in your garden you could use
'refuges'. These are flat objects placed on the ground in sunny spots
creating a warm 'refuge', attractive to slow-worms, common lizards or
grass snakes. A sheet of corrugated tin or a piece of roofing felt would
do the job where space allows, but slate roof tiles would be less
obtrusive in smaller gardens.
Successfully attracting lizards and grass snakes into gardens is pretty
tricky, since it depends largely on whether there are any populations
locally. However, there's nothing to stop you trying - at the very least
you will attract lots of other wildlife in the process.