Yes he did:
https://www.bbc.co.uk/news/live/world-52793960
I thought he said his wife was concerned that his eyesight had been bad while he had been ill and she had no idea if it would affect his driving now so he drove for half an hour to check if he could see properly while he drove. I have no idea if he is telling the truth or not - I am not sure how else you would check if your vision was affected while driving without driving for a distance but it seems suspect that he went to a local beauty spot by accident. I think it was wrong that he and his wife and son would get out of the car and sit by the river during lockdown instead of going straight back to their cottage - he should have realised how bad that would look if the public became aware of it.
I get that he has a 4 year old child and that during the 14 day isolation period people were permitted to go outside in their gardens, so I can understand why he went for walks in the nearby woods on his parents' private land with his wife and child. But after the 14 day isolation period, any outdoor 1 hour exercise was supposed to be close by, not a 30 minute drive away so I do not consider that as reasonable.
I can understand his reason for driving to his parents' farm - in this age of increased reports of sexual abuse of children I would not trust any old neighbour or friend with my 4 year old if my children were that young, especially if I thought there was a chance that both parents might be incapacitated for a long time or die. I would want my 4 year-old to be with close family such as a trusted sister and nieces on private land with big gates that could keep out Press intrusion.
The Government guidance said you can leave home to care for someone vulnerable during lockdown - and a 4 year old child is someone vulnerable that needs protection and if adequate protection was a 256 mile drive away, I would do the drive. I would put my 4 year old's interests ahead of the public's perceptions and I would not feel responsible for other people not obeying lock down rules because of their perception of my reasons for driving to protect my child. The Government guidelines require us to use our judgement when caring for vulnerable people so I would follow the guidelines by using my judgement and put the interests of the vulnerable person I had a parental duty to protect ahead of the public reaction to my decisions.
My husband and I left home during lockdown and drove to his mother's house every day to be with her as she all alone and was dying from vascular dementia, bed-ridden, sleeping for most of the day and night, unable to eat or drink and her primary carer had been suddenly admitted to hospital with pancreatitis.
I am not buying the argument that Cummings should not have taken the option available to him to protect his son (away from Press intrusion if he or his wife were admitted to hospital or died) simply because there were single mothers in similar situations as him who did not have the option of driving to a cottage on private land to isolate near their sister and helpful nieces who would care for their vulnerable child if necessary.
And one of the other questions asked by a reporter at the Press conference was equally meaningless - the reporter said other children had been denied cancer treatment due to lockdown so why should the Cummings offspring merit any special treatment by being cared for when vulnerable. The Cummings child did not have cancer and receive treatment for it so not seeing the special treatment referred to in the question. If other parents had been prevented from driving long-distance to a trusted sibling. niece to care for a young child in case both parents succumbed to a potentially life-threatening illness, the reporter might have had a point.
Of course we do not know if the details in the Cummings story are accurate, but in the absence of evidence to the contrary I do not see that what he did was unreasonable.