complicated working tax credit entitlement query...

hbgirl

i am asking on behalf of my ex-boyfriend. here is the situation (i apologise in advance as i fear i am going to make it more complicated than it needs to be!):

he is 27years old and currently single. he is currently employed 30+ hours per week and earns £18,000pa gross since i think around sep10. i believe he currently earns too much to get tax credits, but isn't it based on previous years income?

he was previously self employed. he hasn't yet done his tax return for 09-10 so doesn't know what his income was for that period (yes, he does keep books but not very well, will be relying on accountant to get the actual figures!). however, by my knowledge of his income at the time, and his previous years self employed income i think it would be at a level to be entitled to wtc.

however, when looking at previous years income for wtc - will they look at my income also for the whole year, or the periods we were together? my income is too high for wtc.

from april 2009 to november 2009, we lived together. but we split up in november 2009 and have lived seperately ever since.

so from november 2009 up to when he got his current job, he was on a low income.

should he have applied for wtc then? his accounts for 09-10 will done by end of this month - if this show a low enough income for wtc is it worth him applying now, or is too late? what period income do they look at when claiming, and when is the claim effective from (is it backdated to what should have been entitled to for the year?), how long is it paid for, he would need to make sure he didn't get too much and make sure he stopped claiming when his current is taken into account in the future???

sorry, although i do work in benefits (housing benefit) i am completely bewildered by tax credits!

thanks in advance for even reading this far!