Thanks everyone for your replies.

We used to let him in the shed but after he started defecating in there we keep it closed. I suppose we open it again.
He's actually been out for the past 6 hours today by his own free will as I have been home all day and been in the garden every hour or so.

That's all very well but I didn't think that cats needed a litter tray during the night if they were let outside before bed and first thing in the morning - as the only other cat I know doesn't. Also he was fine for months without one.

Thank you. I'll see what can be done.

All cats are different. As he's quite young he may be nervous at times or feel vunerable when going to the loo hence fininding somewhere 'safe' to go that is more covered.

You could even put a litter tray in the shed for him as well as some blankets so he has somewhere to shelter if he is out in the day.

Alot of litter sold today is alot better than years ago, easier to clean, less smells, etc as long as you do change it regularly.

As suggested there are lots of different types of litter boxes now - covered ones are great, they stop litter going everywhere & keep any smells more contained. Have a look on Amazon or Zooplus (they are good & I thik do a 10% off with your first order)

One of my cats still comes in to go to the toilet, in some ways I prefer this as it means I don't have cat poo in my garden (I have enough problems picking up after the dogs!), & I can keep more of an eye on his toilet habits (he used to suffer with cystitis).

Hope you can sort things out

Try him with a tray, if he doesn't need it he won't use it and then a tray full of clean litter isn't offensive at all. I can understand the reluctance with a tray, I am the same because my cats always go outside and have a cat flap to do that at any time but obviously you don't want him to be in distress. It is a complete pain that you can't train cats to go on demand like dogs, I always feel sorry for mine if I have to take them in the car to the vet or the cattery as I can't tell them to go before as you would with a child and there has been the odd accident in the cat carrier which isn't pleasant for anyone.