Thanks for the info, I live in Yorkshire and although almost 70 years young have not been spotting all that long, have never spotted in the London area so am thinking not much freight on Sunday so try to get the maximum variety of units. Richard
Clapham Junction will definitely still have a good variety of units on a Sunday. You should be able to see class 158 / 159 / 377 / 378 / 387 / 444 / 450 / 455 / 456 / 458 units. You should also be able to see some of the brand new class 707 trains in the yard visible from the station.
If you are interested in freight trains then there are still some freight trains going through Clapham Junction and the surrounding area next Sunday.
East Croydon will definitely have a good variety of units on a Sunday as well. You should be able to see class 171 / 375 / 377 / 387 / 455 units. Southeastern are also diverting through East Croydon next Sunday which should also make it more interesting.
You could always always spend time at a few different stations around the London area to get the most variety possible.
If you are not already aware of these websites you may find these websites useful:
RTT -
http://www.realtimetrains.co.uk/search/advanced - Click on "extra search options" then for "what time" select "00:00 to 23:59" and then you can select the date and the name of the station you are going to be at. This will then show you all trains calling at and passing through that station on the day (both passenger and freight trains).
OTT -
http://www.opentraintimes.com/maps - Click on the map for the station or area which you are going to be at. This will then give you a live map showing the locations of all of the trains in the area (both passenger and freight trains).
Hope you enjoy your visit.