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Check your local area. Where in the UK are you living?
There will be some wood retailer. It's best to go there, they have the best sort of wood and are not any more pricy than any home store. Also check the rest pieces box in the home stores and at the wood retailer, they often have (for us!) suitable pieces in there for a small price.
Try Birch ply, Beech ply (love it!). Also Beech 3/4" and Alder 3/4". Spruce is pretty rough, I don't like it much.