Overgrown cordon fruit trees

You should only cut into soft green shoots during the growing season - cordons would normally be pruned by cutting back most of the new green shoots during July. Well-placed shoots can be left unpruned.
Winter pruning should be minimal for cordons if they are properly summer pruned, since summer pruning enhances fruiting in the following couple of years, while winter pruning suppresses fruiting and enhances re-growth.

If you cut into older wood during the growing season, there is a considerable risk of canker infection getting into the tree. Some varieties are fairly resistant, but some are very easily infected.
I suggest a thorough examination of the pruning wounds during the winter, to look for brownish-black, sunken areas of bark that indicate canker - and prune them out before the cankers spread down the branches in subsequent years.
In optimum conditions (warm, damp), I reckon that a canker can enlarge by a couple of millimetres (1/10 inch) each week on susceptible varieties.

Also, if you've cut them back hard, you might have a reduction in fruit next year due to the loss of large numbers of fruit spurs.
However, summer pruning encourages fruit spur formation, so the net effect may be nil.

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From what you say, it sounds as if you've changed them from fruiting columns, into a tree shape.
Apples tend to grow from the top, with the strongest growth being at the top of the tree.
Removal of lower branches encourages the tree to grow upwards and the lower branches often won't re-grow much because the top of the tree secretes a suppressing hormone that reduces vigour in lower branches to stop them competing with the leader.
Removal of upper branches encourages the trees to grow outwards and redirects energy to the lower branches. By removing the leaders, the suppressing hormone is disrupted and lower branches will grow more.

Lower branches, or branches growing almost horizontal, tend to be more fruitful. Upright branches don't tend to fruit much - they just keep growing.

If you've converted your cordons to trees, beware that their roots have enough anchorage to support the canopy. Many cordon rootstocks have quite brittle wood, meaning that if the tree has too much topweight, the trunk can snap off at ground level in strong winds.

Hope there's some useful stuff in there.....

Thanks for the reply .
The four trees- apple, greengage, pear and plum - were already massively overgrown when i bought the house.Nothing had been done to them in years and as they had been planted so close together the branches were growing from one tree to the next, there was very little light and air and the greengage had huge inch and half diametre branches growing from below.Only the pear and plum were fruiting and not much at that.The greengage in particular was very dense.
My intention was not to leave them growing as normal tress but to take them back to how they should be over maybe a couple of years.Having said that it might be more prudent to let them grow as trees but restrict the size by pruning every year.
What i have done is removed all the lower branches and pruned the ones at the top to about 18 inches - 2 ft,removing some altogether to allow light and air in the middle
I'll keep a look out for canker during the winter months

Ah, I didn't realise that there was a gage, plum or a cherry. They are not normally grown as cordons.
Plums gages and cherries need to be pruned during the growing season, so you're OK there.

the gage was the worst of the lot.I t was like a very dense bush you couldnt see through .I was quite severe with that one