....and to wonder how on earth I achieve this without ruining the business relationship?
I work freelance for a firm and have done for 4 years. They have always been rubbish at paying me, despite our initial agreement that I would be paid within 2 weeks, but I have generally always been busy working for other firms who settle my invoices quickly, so it's not been too much of a problem. I know they will always pay me eventually so I've generally been patient.
I've been pretty quiet with work recently and I really need the money now (my husband and I aren't even buying each other Christmas presents this year because of finances - this first time in 12 years of being together we have had to do this 
I have around £2k outstanding, some of this is from 6 weeks ago but some of it is from July! I have sent a couple of emails recently which have been ignored so I spoke to her today and explained that I'd been quiet recently and my cashflow was suffering. I was told that she was owed a lot of money herself from other companies (and therefore struggling herself) and would do her best to pay me this month (the tone and the way this was said made it clear to me that I have more chance of a visit from the Pope this month than I do of receiving any money!)
I don't think I'm being unreasonable to want my invoices paying, despite the fact that I have previously been patient in waiting for payment, because I've been in the financial position to be patient. I now really need the money but don't know how to go about it - I'm worried that if I start insisting on payment, therefore appearing to disregard her financial issues, that I will find myself losing the existing and future work with this company, something I can ill afford to do.
I know they are happy with my work as they told me recently, but I've had a disagreement recently with one of the other people they employ on a freelance basis and spoke to the boss about it. This has been resolved and isn't a problem for me but I'm worried that they will think I'm just trying to make waves because I didn't like the response I received when I raised my concerns re: the colleague. This certainly isn't the case - I'm just skint and really need some cash!