It should be planted in the ground in a nice sunny & open location. Maybe bring it to the park. I have giant oaks outside my house that are over 100 years old and over 80 feet tall. They drop their acorns everywhere, but protect my house from storms. The discolored leaves indicate a nutrient deficiency and it's outgrown that small pot. The only answer is to plant it so it can develop its deep extensive root system.

Sorry Bath but looks to me not big enough to have outgrown the pot yet - easy to check by carefully upending the pot and checking whether its getting potbound. If at all possible I'd delay planting out until we have some reliable rain.

No need to apologize to me. It's not my tree. You're entitled to your point of view. I'm pull up saplings like this everyday, even during drought.

My daughter has been given an oak to mark a milestone birthday. It's a bit bigger that this one. We have put it into a slightly larger pot than it came in and watered it well. It stands outside in semi shade and I've suggested she plants it in the autumn when we've had a good dose of rain and when the tree has dropped its leaves and is dormant. I hope it was a sensible thing to do! I'm no expert, it's just what I thought might be the best way to deal with it. I told her she will also need to make sure it doesn't dry out once planted for the first year or so.

What it really needs is a deep, narrow pot - like most trees, it puts down a long root initially, and it can't do that in that small pot. Use something like the pots a good sized clematis comes in when you buy them - much deeper but not really much wider than the one its in.

It looks to me like a leaf fungus. My first suspect would be anthracnose, but it might also be Phytopthora ramosum.

Oh great, that's a goner then if its either of those...

Anthracnose is treatable, but the other is less amenable.
For anthracnose, I would use either Bacillus amyloliquifaciens, or propicanazole. Not sure what's available in the UK, though.

Thank you so much everyone. Its my daughters and she needs to keep it in a pot as they are planning to move house. She very fond of it
Please can anyone suggest a remedy we can get in the UK

Ps sorry should have said I’ve just checked the pot and can’t see any roots coming out the bottom and there seems plenty of room for it at the moment

Could you take it to a good garden centre and ask the tree specialist? They should be able to identify the problem and sell you something to remedy it. Otherwise stand in a semi-shaded spot, keep it watered and hope for the best. Bamboo mentions the taproot, which might not send little bits out of the bottom. It's more likely to curl up or round so a deeper pot is a good thought, as she suggests, so that the root can develop properly.

If the worst come to the worst autumn is coming together with a fresh crop of acorns...

That’s brilliant thank you - I turned it out of the pot briefly to have a proper look and the tap root is curled right round. I was looking for fibrous sort of roots! I’ve got a clematis pot to put it in , should I try to straighten the tap root or will it do that itself?

No, just leave the root as it is, though dislodging any loose soil from around it isn't a bad thing prior to potting into the clematis pot.

Thank you so much. It’s now in a clematis pot ,watered and in a shady place till it gets cooler
I’ll report back on how it gets on

Good luck, Sunbeam, but I'd plant a few more acorns with Lucy this year just in case!