We rotted horse or cattle manure can be dug in during the autumn with the emphasis on 'well rotted', peat will not help your soil and soil improver or composted bark if you can get it.

Anything you can find that will add bulk and humus will help. On very light soil I would wait until the early spring to add manure as although it will help the soil texture whenever you add it some of the nutrients will get washed out during the winter in a very light soil.
Whenever you add manure make sure it is completely rotted first.
If you have a local source of autumn leaves you can lay them on the lawn and mow them, and then either compost them or spread them as a thick winter mulch. they rot down twice as quickly if you chop them like this. They will take some nitrogen from the soil when they rot but they will improve the texture greatly and you can always add a little nitrate if you want - or grow peas and beans, which will do the job for you if you leave the roots in after cropping.

It would also be a good idea to do a soil test - you can buy kits quite cheaply. On sandy soil you might find there are very few nutrients there, so you will know what needs adding.

Often on sandy soils, simply laying the compost and organic mulch on top of the soil will do all of the soil conditioning that you need. Worms and rainfall will gradually move the organic matter into the ground, while the coating of mulch on top helps keep the soil moist, and helps adsorb nutrients.

Thank you all for your replies. The advice is much appreciated.