I plan to submit in September, and so am in the process of writing up at present. I just had my annual review and it knocked the wind out of my sails. Previously these reviews have been a formally to check that I am happy with my supervisors and they are happy with me, and no nasty surprises. However this one was weird, seemed to be going fine, the convenor had lots of questions, I thought I dealt with them ok, I was then asked to leave the room while the convenor spoke to my supervisors, I was outside the room for ages, then I was asked to go back in, there was no mention of what had been discussed. The review continued on to completing the necessary paperwork for the faculty, all still appeared fine. The final page of the paperwork was for the convenor to summaries the recommendations of the review, he began by commenting that I should continue on making good progress towards submission, then the weird bit. The convenor got very funny, mentioning things that obviously had been discussed while I was out of the room, suggesting that all drafts be sent to my supervisors (they have them all already) and that all my raw data sent to my supervisors for them, to look at, as the analysis is not up to much. That I should meet with my supervisors asap to go over this before I write or rewrite anymore. He also mentioned something about not having enough for a PhD in a very vague way. I have felt that I have had a good relationship with my supervisors and have offered my data for them to look at before and was told it was not necessary, they have never mentioned any concerns about the lack of PhD worthy info. I am really confused. It totally took me by surprise and I was not given any opportunity to comment on it at all. I am now really worried about failing and only have 4 months to try and do something about it. Why have my supervisors never mentioned any of this to me before?
I now have no idea if any of my research or the 60000 words I have written are any good at all.

sounds rather depressing. you kinda felt stabbed in the back didn't you?
to be fair, the supervisors may not know this themselves.
so now that you've only got 4 months left: clear your head, go and have a nice long chat with your supervisor (s).

if they are still not helpful, I guess you will either have to ask for some ideas from your colleages/postdoc in group or anybody doing PhD or recently finished PhD.
Perhaps have a quick look through their thesis and see what kind of data they show (in terms of details relative to the subject) and compare that to yours. work out what you've got to do for improve yours. I'm sure you've got most of it there. What he meant could be just some minor detail that would enhance the PhD much more which may be lacking.

It is extremely difficult to be starting any experiments within four months but it is feasible. some people does that while they've still got to write their thesis! some just don't really have any choice really.
Don't lose hope! At least you still have some time!!

it is pretty tough having supervisors who cannot guide you so well but in this case you've just got to kick it and keep going.