I contacted Network Rail yesterday after receiving complaints like the one below:
Network Rail have responded and agreed to provide two security guards, one on either side of the bridge, from 4pm to 4am, until further notice, starting asap.
Streatham Vale Bridge Closure Blog
Trying to get some sense out of Network Rail & Lambeth Council
Streatham Vale Bridge Closure Blog 
I work a shift pattern, and travel home at different times, this week I have been using the walkway at approx 2330hrs and there is no sign of any security guards nearby, all the workers are congregated in Homebase car park. I do not feel safe walking through the **tunnell** and using the bus service puts another 20mins or so on to my journey so I don’t get home until after midnight
Hi Phyllis, I spoke with Network Rail last night and we’ll speak again on Monday. It looks like they will provide additional guards for the bridge and ensure the existing guards are doing what they’re supposed to be.
Thanks,
I walked home that way again last night with a friend, we then waited for the shuttle bus as she lives further down the Vale, this was midnight, the bus scheduled for 0025 did not turn up so we had to wait until 0045hrs for the next one, while waiting we did see 2 males who looked like security guards they were together and were hanging around outside Streatham Vale entrance to the station, not really keeping an eye on the **tunnel**
Regarding the times they say they will supply these guards, I do not think up until 4am is acceptable, it should be later, as many people (including myself) leave home at 5/5.30am some mornings, not very pleasant walking through *tunnel* at this time.
I’ll send this feedback straight to the manager responsible. We have a meeting on Monday, and hope that they can resolve the security problem next week.
I’ll also get on to TfL about the buses. Thank you for letting me know.