So my satsuma tree seems to be doing fairly well and grew a lot of new leaves a few weeks ago, but now it has stopped and looks to be resting.
So:

1) Do they need some sort of dormancy? So many months below a certain temperature? How should I keep them indoors over winter?
2) I eventually need to re-pot it. It is grafted onto poncirus but I have heard of citrus compost in the past. Do I have to use a special compost or can I just use a quality multipurpose?
3) Feeding - Do I need special fertilizers or will any liquid plant feed high in P and K and low in N work (tomato feed?)

Thanks[/list]

1. Now that your tree has finished producing new leaves, it is now producing new additional roots to supply the new growth.

2. When re-potting there are many types of mediums you can use. Whatever you use BE SURE it provides GOOD drainage. A couple good mediums are 50/50 cedar mulch/peat moss; a mix of 3 parts pine bark chips with 2 parts peat moss and 1 part coarse sand.

3. Container citrus trees absorb fertilizer in a 5-1-3 ratio. Meaning for every 5 parts Nitrogen that the root system absorbs, 1 part of phosphorus will be absorb, and 3 parts Potassium. A fertilizer with the formula 25-5-15/TM (a 5-1-3 ratio) is an excellent fertilizer, but in England I think you will have a very difficult time locating it. If not, try to locate a fertilizer with higher levels of nitrogen, and potassium, and a low level of phosphorous. Whatever fertilizer you use BE SURE it also contains trace minerals. Good luck to you and your tree. - Millet

Do I have to leave it somewhere cool in winter to have dormancy?

Citrus trees are evergreen, and don't really go dormant like deciduous trees, but at temperatures at or below 55.4-F (13-C) all citrus tree growth stops. You can store your tree in a "dormant" type condition over the winter months if you wish, but you certainly don't have to. I keep all of my many trees in a growing condition all year long. - Millet