Freelance work and tax credits any tax geniuses out there?

[SarfEast]

I have recently undertaken some freelance work for the next few months, i invoice the company at the end of every month. I understand that at the end of the tax year I fill out a self assesment form and pay roughly 25% of what I have billed throughout the year. We are entitled to tax credits and have just been notified of how much we will be getting this year.
When do I tell them about the freelance work? I have no idea what I will be earning for the coming year...
any help would be appreciated

Not a tax genius so someone else may know more than me!

As far as I understand, you should estimate how much you'll be earning this year, incl freelance work. If you don't, you'll be given too much in tax credits and when it comes to next year (when you have to declare how much you really earned), you will owe money back to the tax office and end up out of pocket.

Can you just come up with a rough figure of what you expect/ hope to earn?

Absolutely no expert on tax at all, but this and this might be helpful.

Ahh brilliant thanks all...

will read all the links and decide what to do...