Death of owner, property not registered

My parents bought their house in the 1960's as a new property and have been the only ones to live in it. My Dad died in 2011 and I was the executor of the will. I understood from my mum at the time that they both owned the house and there was no mortgage so didn't believe I had to do anything. However we have found the deeds and they are just in my deceased father's name. The house isn't registered with the land register. I want to change the name on the deeds to my mum as per the will everything went to my mum. How do I do this, do I have to register the house first before completing an AP1 form?

LC McFarlane - it was quite common in the 60s/70s for just the male to be the buyer/owner.
Just the one application now, a compulsory first registration to register the transfer by the executor to your Mum as appropriate
The legal ownership has, since his death, remained as part of his estate. Any transfer now will be compulsory to register for the first time

HM Land Registry public guidance - GOV.UK (www.gov.uk) - have your say to help us to improve the support we provide 
 

I understand that this can take over a year. My Mum has a terminal illness, what would you suggest we start this process now knowing that during this time my mum may pass away?

LC McFarlane - so sorry to read that and yes there is a backlog of this type of work. 
My recommendation would be to seek wider legal/financial advice as to what's 'best' in the circumstances as far as what happens next re her terminal illness.
For example might it be 'best' to transfer the legal ownership into someone else's name or in joint names or a trust?
No reason not to transfer it into her sole name though as well if that's what is wanted and if she sadly passes before registered then that can be dealt with as appropriate
Sorry to use words like 'best' in such difficult circumstances but please do consider that wider advice as well