Home office and DNA

[Mkuki]

Hi all.i came 2 the UK in 2001 and claimed asylum.my claim was refused n i am a failed asylum seeker.in that time i met a british man n have 2 british children 4 n 2 yrs old. December 2011 i made an FLR(O) application on the basis of family life i.e living 2gether as a family.last week home office asked 4 DNA 2 prove that the children are ours.anyone ever come across this? DNA tests are expensive am at a loss on what 2 do.pls advice.