By-passes are being built all over the country and leaving some very unhappy property owners in their wake.
If there's a compulsory purchase order (CPO) placed on your uncle's property, his rights and ability to get a fair compensatory package will diminish as compared to say, his property going on the open market. Also, if part of a private house (inc garden) is taken, it is dealt with in a different manner than if the council are taking argicultural land. As well as that, he may discover that if the corner of his garden which is being taken will only form part of the verge or hard shoulder of the new road, his compensation will be less than if the new road surface will actually cross where his garden is.
Having some experience in such a situation, I would advise getting a good solicitor experienced in such matters working on your Uncle's behalf and also a professional valuer. Bear in mind though that such advice, while necessary, can be expensive. Double check whether those professional fees will be covered by the authority looking for the land and if so, to what extent. They may only intend to cover the professional fees for the actual transfer of ownership of the piece of land. You dont want to end up having any financial compensatory package swallowed up by professional fees. If the Council agree to pay fees, especially for a valuer, be confident that his/her advice is looking out for your Uncle's best interests, not just the easiest option for the Council.
The laws governing CPOs is grossly unfair, archaic and badly in need of reform.