Actually, jake, nobody has to invade by force. Our membership of the EU and our ludicrous immigration policies will achieve by stealth what countless would-be invaders have failed to do by force throughout the centuries.
The UK government cannot determine who does and does not come here. Once here they are free to plunder our wealth via the benefits system. They have to be housed at public expense if they have nowhere to live. They are free to commit serious crimes and cannot be removed after they have served (half of) their sentence. With the exodus of people from the UK seeking to retain as much of their hard-earned as possible, and the higher birth rate enjoyed by immigrants, eventually the incomers and their descendants will be able to outvote the original population and the “invasion” will be complete.