Ssp and tax code

Hi,

I wondered if anyone could help, im struggling to find info online. My husbands tax code in December was 1150L, he has been off sick since January and claimed SSP until August and nothing since, we cant get benefits, however we noticed on his pay slips from when he was getting SSP his tax code was 799L and he doesnt recall getting a letter explaining why. Does anyone know if SSP makes it drop or know the reason why it might have dropped since hes stopped earning?

Thanks