OMG! This could be serious!

How big can it be?
Can you cut it in half and do it in 2 stages? Or bung it in the oven in a roasting pan half filled with water?

I think there will be a popular vote for you to Curse the Gammon again, phoenix

Mine won't go in the slow cooker either so I'm resorting to the jam saucepan.

A very large supermarket foil container would surely do the job, designed for a large turkey but with a foil cover.
We sometimes agonize too much.

I’m out the whole of Christmas so no cooking for me

I used to cook a gammon joint but now I buy some slices of ham instead. It tastes better than mine ever did and we're not eating it for evermore.

Cum on now phoenix! Don't be a weakling ? Can't you squish it a bit ?️‍♀️ bash it with a hammer ?, pound it into submission. It must fit. Put the cooker on the floor put the gammon on top and jump on it till it fits.
None of that works .... then I guess cursing the gammon is the only option left .... have you thought of becoming a vegetarian? #innocentface!

Crafting

I hate gammon I would be very happy to bash it with a hammer for you.

Put it on a diet? If it really works at it, it could lose 2lbs by Christmas!

Cut it in half.
Cook half, freeze half.
A whole gammon means you will still be eating it at Easter.

Oh No!

I haven't bought one yet so thanks so much for the warning phoenix

Now, simmer or roast ---
That is the question.
Whether 'tis easier to suffer the agonies of burnt fingers
or to take a knife against the troublesome joint

Slice some steaks off until it fits!

I always cook mine in a little water in a large roasting pan in the oven. completely covered with foil. Basically steam-baked and always turns out beautifully. I give it 30 mins per 500 grams/1lb plus another 30 mins. Start it off fairly high for 20 minutes then turn it down to medium.
Let it cool in the pan unwrapped then peel off the skin and glaze it or coat with breadcrumbs as required.
The ham juices left in the roasting pan are wonderful for soup, or stock as long as they're not too salty and they set to a lovely jelly.

I can't wait to prepare mine! I used a recipe from a tv program last year and it was fantastic. Boil for half cooking time in water and orange juice, then drain and cover with orange marmalade and roast till tender. The whole family have asked me to repeat this year. I could have eaten the whole joint myself!

Put it in a roasting tray and pour in some water or cider to a half inch depth. Cover tightly with foil and bake at the bottom of a very low oven overnight. In my last house, we had an Aga and I often used to put gammon in overnight and wake to the wonderful smell in the morning. FAB!

I should add that the temperature for overnight baking would be around 100 degrees C.

Try cooking it in a roasting bag, add a couple of cups of orange juice, pop in the oven. About 30 mins from the end, take joint out of oven, remove bag and juice....go careful, it's easy to spill everywhere! Cut off the rind and some of the fat, and generously coat the remaining fatty surface with brown sugar. Pop back in the oven to brown off. Lush!

How big is it?

Last year I cut my 6kg (13lb) gammon in half and stuffed it into the slow cooker. I could not get the lid on but made a snug lid with kitchen foil and it worked really well.

I have also invested in a 10 litre pan from IKEA in case it doesn't fit this year

Your DH might buy you a bigger slow cooker this year if you moan enough.

Do remember to turn on the slow cooker. Two Christmases ago we had a guest. We enjoyed the starter and main course, went to get the pudding out of the slow cooker where it had been steaming all morning I hadn't turned it on. A blast in the oven seemed to work! Tasted fine.

13lb?

Your slow cooker must be larger than mine!

Can’t have one, husband is on a low salt diet so just buy a couple of slices for myself

I always pressure cook it, the pressure cooker is plenty big enough and the and the glaze finished in the oven for 20 mins or so.

We went a bit bonkers with the gammon this year, too, and it is a big beast. I will braise it in the oven in a large foil turkey tray, surrounded by chopped veg. Half of it will, I hope, go home with my SiL on Boxing Day, otherwise we will still be eating it next Christmas! Why on earth do we do these things?