I know what you want to say, and it is largely correct, but I won't let that get in the way of pedantry. The UK does have a constitution, which is often referred to as "unwritten". This is a bit of a misnomer, as most of the constitutional provisions in the UK are written down somewhere. For instance, most of what would be the equivalent of the US Fourth Amendment protections against unreasonable search and seizure are contained in the Police and Criminal Evidence Act 1984. The UK constitution is not codified, and there are no framework constitutional principles (well maybe Parliamentary Sovereignty ), but it does exist. There are rules and processes that govern what become laws. It's more that Parliament can decide to remove any rights by repealing any enabling legislation, PACE, HRA, whatever. In the US, rights are supposedly natural, and cannot easily be taken away by government.
Certainly, in the UK Parliament has not granted the citizenry any general protection from self incrimination. While there are laws against torture and other practices that could lead to malignant self incrimination, even the police caution when being interviewed reminds you that "You do not have to answer any questions, but it may harm your defense if you do not now mention something which you later rely on in court." So you definitely do not enjoy the same broad protections from self incrimination in the UK as you do in the US.