Moving a fruit tree

I'm no fruit expert but I do know that if you need to move something now is a good time as the tree will be dormant. However you will need to take out a large rootball and put it in a large pot, I'm thinking a half barrel. It will need a lot of watering in a pot, not a problem at the moment (!) but you will need to keep an eye on it.
I'm intrigued as to why the species and variety are secret. Has it ever flowered or fruited? If so from a bit of a web search you might be able to work it out yourself, as knowing these will help you to know how to care for it. If you have pictures to post on here someone might be able to identify.

Go for it! Winter is the right time to move/transplant trees. I regularly move 1,2 and even 3 year old apple and plum trees from pots to open soil and vice versa, and have never lost any. When moving out of open ground, I fork round and under the tree to the depth of just 1-2 spits and gently prize it up, trying to minimise the snapping off of roots. If the tap root is deep it is pretty likely to break. However, although this is a bummer from the point of view of anchorage and potentially for water extraction from deep in the soil profile under severe drought conditions in open soil, the impact on subsequent nutrient uptake is likely to be minimal, given that the majority of these are absorbed from the upper horizons of the soil. Because of this, I'm much more concerned at lifting a young tree with the maximum intact length of fine roots in the topsoil as possible. I also try to leave this (rhizosphere) soil attached to the roots with as little disturbance as possible. The transplanted tree will grow more roots in the spring, provided it's reasonably well cared for (after injury/loss of either part of shoot or root, many plants tend to initially put new growth into re-establishing the lost part and regaining their former shoot weight :root weight ratio).'Staking' for a few years will overcome the loss of anchorage provided by the tap root, although a tap root would be pretty useless in a pot anyway, wouldn't it?.

1. Yes, you can move it. Moving it while it is dormant is the best time. Moving a tree with leaves on may kill it as the damaged roots cannot supply water or nutrients to the leaves, so the leaves and shoots will often die. To move a tree while it's in leaf requires a lot more thought, planning, care, skill, effort and time - and is not recommended.

2. Most trees can be transplanted in winter.
The older a tree gets, the less well it tends to transplant. After several years it may suffer severe root damage when dug out, as a several-year-old tree can have big thick roots which have to be sawn or loppered. I moved a three-year-old MM106 apple tree recently and the roots were as thick as broom handles and had to be sawn off. The trauma to the roots may allow fungi to invade the extensive wounds and may eventually kill it. Don't water "wounded" trees immediately after planting and don't plant them out in saturated soil.

3. Mostly assume that it's OK to move a tree in winter, but never say "always" and never say "never" as there may be occasional exceptions. If in doubt: ask!

4.
Putting it into a pot is OK in theory, but in practice I suspect the root system will already be far too large - unless the plant has failed to thrive and hasn't grown any more roots than the day it was planted. The fact that it's three years old but only 1m high suggests it's not happy about either the soil or the climate - or maybe diseased.

I agree with the other posts, now is the best time to move it. Normally when transplanting a 4-year old tree you would need to cut back the top growth very substantially (to allow for the inevitable loss of root), but the thing that seems very strange is that the tree is only 1m tall, yet is 3-4 years old. A 1-year apricot would normally be nearer 1.75m tall when supplied from the nursery, and apricots are usually very vigorous. Whilst it might not fruit reliably as far north as the Nottingham area, it should still be growing very happily.

You may find that the shock of being moved (to hopefully a better sunnier spot) might kick-start it into growth.