Your stage 1 puzzle will have 25 of the 26 letters, just one remains, nowhere to be seen, and you need to find it at your next destination.
Luckily, the blue info board at location 2 has the letter you need on it to show you the way. From here it should be a QEF.
Stage 1 can be done 24/7, stage 2 only during the daytime.
This cache was kindly authorised by LB Ealing Council.