My post count is Majestic
To be honest although this doesn't sound good I don't see that you are in trouble yet. It sounds to me like someone has overstepped the mark or have been taking the piss so the client is just ruffling feathers to get everything back in order. We have had wfh bans and a reminder of core hours twice at one of my clients which got relaxed shortly after. I think the fact you have done this historically without a problem proves the client doesnt see you as a permie. He is just kicking some butt which will relax once the dust has settled.
What I would do however is gather as much evidence as possible to prove your old working conditions just in case this isn't a passing phase. Copies of mails with your addition on, previous evidence of odd hours you worked, photocopy of your security pass if it is different to permies, anything you possible can just in case.
If you are so worried try getting a Confirmation of Arrangements letter signed so you have it in writing the general agreement is still in place.
'CUK forum personality of 2011' - Winner - Yes really!!!!