I recently bought a 6ft Tree Fern

I had one of these and planted it out in full sun with no problem. The real problem came in the freeze of Dec. 2010. Although the crown was stuffed with straw and it was well fleeced I am afraid that was just too much cold for it. I see you are in Cheshire so can expect, eventually, a really cold winter. It is therefore probably better to keep it in as large a pot as possible and if things look flaky weather-wise to get it undercover. Fortunately, they are slow growing but yours is already large and will be difficult to move in and out of a glass house. I did hear of one keen gardener/d.i.yer, with one in the ground, who made a sectional poly-glass cover that could be erected and taken down as necessary. Would you call it a cold frame or a greenhouse? I don't know. That could be difficult but these are not cheap plants and it may be worth the investment of time, effort and cash. Good luck and do keep us informed what you do and how it works.

If you must keep it in a very large pot, then rich humus soil (I mix in mini bark to compost), and keep adding leaf mulch to keep the soil damp - you will also need to add rich humus and bark and leaf mulch if you placed in ground. They are rainforest plants so:

1. Dappled shade
2. Damp but well drained soil.
3. They need shelter from the wind - in a middle of a forest the wind is weak if it gets there at all.
4. Neglect them - if you do all above then leave it, they live longer than we do, so enjoy.

I planted one in a pot in Bath some years ago - the tree was about the same size as yours, but the pot wasn't - we used a heavy, stone, square pot about 2.5 feet deep by 18 inches wide. We initially wedged it in place with cobbles to keep it upright. You will need a pot of a similar size and weight to the one I mentioned - it needs to be heavy or its at risk of blowing over in a high wind because of the height of the tree. The larger size of pot will also 'balance' the overall look of the tree/pot from an aesthetic point of view, so that it doesn't look as if its temporarily been crammed into something way too small. Use John Innes No. 3, or a mix of that and multi purpose.
As for conditions, I wouldn't plant a tree fern in London where it was in sun at midday, but maybe where you are, the sun is never that strong in summer, though I suspect it probably is. Dappled sunlight's fine, or sun late afternoon, but not during the middle part of the day.

Thanks Sarraceniac, Kildermorie, Bamboo.
I lost a smaller one during the same bad winter we had but i haven't given up on it and planted it in the ground just in case. I have dropped it twice now trying to move it and took a large chunk out of the top of it. So maybe that idea of making a greenhouse just for it is a good idea i think i might make one in the summer ready for any bad weather.

The trouble with large expensive plants is that they need large expensive tubs but hopefully i am going to go and try and find a bargain tomorrow and buy as big as i can afford.
Thanks for all your advice i will buy the compost and mulch you all suggested and try and find the right place in the garden to put it.
Regards
Bill