I believe the regulations regarding Working and Child Tax Credits are different from those for other benefits. There are definitely immigration regulations for these tax credits which can give people who are in some categories of "Immigration Control" access to them provided the spouse or partner has a UK passport or is someone who is not subject to Immigration Control.
Whether this will help in your case I can't say, but you need to look into it. You could start by ringing the Tax Credit Helpline (0845 300 3900) and explaining the circumstances. However, unfortunately sometimes the advice given is not as comprehensive as it might be so it could be better to go to your local CAB or other welfare benefit advice centre.