Kryton said:
Sorry but I think you need to expand your client base (and fast) the above are just messing you about.
Not struck on your contract either,

you're on a 'hiding to nothing' I'm afraid.
I've got multiple clients, but I've been working at this one for 7 years (on & off of course). It's just that since the beginning of 2010 they implemented a new system for paying contractors, which works well for their multi-million pound contractors, but not for us small-fry, and the accounts department don't particularly care as their KPIs are around amount & value of invoices paid, so the small-fry ones are bottom of their priority list and get passed around as people go on leave, sick, etc.
I used to invoice directly and knew where I stood regarding terms & conditions, but since they implemented their 'approved supplier' policy I cannot bill directly and have to go through a 3rd party. So I chose the 3rd party that I've already got a sub-consultant agreement with and has worked well with other clients for the last 10 years. It's just that when a problem like this arises the 3rd party doesn't want to lose their 'approved supplier' status by complaining, but I'm stuck with and agreement which means the 3rd party won't pay until their invoice is paid (they pay me the day after they receive payment).
I had the choice a few years ago of moving over to their 'guaranteed payment' agreement, but as I'd not had a problem for 6-7 years I didn't think it was work the extra fees they charge for the guarantee (about an extra £50 a week).
If they don't pay us and we remove our services then they get someone else, as they assume that their under-utilised consultants can do what we do (some of them can, but not as efficiently or with any creative flair). They can't afford to do that to the big contractors as they'll just down tools and you end up with a half-built motorway bridge
I've got other clients giving me work here & there (and one who pays invoices the day after they're submitted), and got a nice lump from my work on the sale of HS1 to the Canadians, but that just helped stave off the shorter & shorter projects, and shorter working weeks (3 days instead of 5) that some clients are running. So for the last 2 years I've probably been on 50% of my normal income - which is already based on a 39 week year (August & December are usually quiet, and then you've got to take off all the bank holidays for the different countries).