mortgage application leeds building society

Hi,
Myself and my partner have just put our application through using an advisor with leeds it has gone to the underwriters but they keep asking for extra documents on my partner, I have had a mortgage for 8 years and he has lived with me for a year due to having a small baby we need more space, my partner has a poor rating no debt just no credit history they had our wage slips and all documents but requested a statement from my partner to prove he pays tax even though says so on wage slips, now the problem he contacted the tax office has received a letter saying he has paid no tax ever he was in his previous job 8 years and just started a new job he was completely unaware as his wage slips states he paid it now his ex employer is being investigated but I am due to take the tax letter tomorrow to be sent to leeds will they refuse us our mortgage offer now thanks for any help