Mum has died and everything goes to dad...

[Achooblessyou]

I don't need to apply for probate as I've managed to transfer joint accounts/house deeds to dad without it. There's no inheritance tax to pay as les than threshold. Do I need to fill in IHT205 (HMRC inheritance tax form)?

You only need to complete IHT205 if you have to apply for probate or letters of administration.

Thanks I thought so but I didn't find it very clear on the hmrc website.

If a married spouse is inheriting then there is no inheritance tax to pay at all. The only time inheritance tax needs to be considered in that scenario would be when the surviving spouse passes and then they would have both tax free allowances applied to their estate before IHT was due (e.g. if threshold was 325k per person then upon death of second spouse their estate could total 650k before IHT becomes due)