The website is careers.walmart.com/SearchJob.aspx though I just did a search and nothing came up for the DC in London either. I am not sure if they are going to be doing any more hiring for awhile. In my interview I was told that the orientation class in mid September would probably be the last one for the year as they are going to be getting busy with the up coming holiday season.
If you are interested in working there I suggest to keep checking the website every week on Wednesday or Thursday. When I was applying that is around the time they would post new positions. Then apply to anything that you would like to get.
In the meantime I suggest you start working out if you don't already and getting ready for the physical abilities test. It can be a bit hard and I doubt anyone that is not active could pass it.
There are three tests. I am not sure what the minimum is to pass but I did pass. In the first test there are 6 milk crates with weights in them ranging from 19 - 55 lbs. You have to pick these up one at a time and walk across the room and put them on platforms that are 3 and 4 feet high. You then pick them up and take them back. You do this for 9 minutes, you cannot stop and you need to move as many as you can.
For next test you have 1 minute to do as many sit ups as you can. Pretty straight forward.
The last test tests your upper strength endurance. There is this machine with bicycle pedals that you kneel at and have to pedal with your hands. You have to pedal for 2 minutes and try to get as many rotations as you can in that time.
I did get the job for orderfiller by the way. I start in September.