Simply ignore TVL/BBC. Their letters are computer-generated and sent out by the hundred-thousand. The purpose of these "official warnings" and threats of "imminent legal action" is psychologial rather than actual. Once this is realised, the letters cease to have any effect or credibility.
The same applies to street visits. If someone called at your door and asked to see whether you had a washing-machine or a food-mixer, would you let them in? Of course not, so why permit TVL/BBC to look for a TV, video or DVD player? People who work for TVL/BBC have no more right to enter private residences than people selling dusters.
Without entry, TVL/BBC have no sure means of knowing whether a house has equipment set up to receive broadcasts. That is why they rely on mass mailshots, declaring messages such as, "This is your final warning". They rely on householders' own reaction to these letters, and on self-incrimination during street visits. Without YOUR co-operation, TVL/BBC is impotent.
What about search warrants? Before a search warrant can be issued, TVL/BBC must satisfy the court that they have "reasonable grounds" for believing that broadcasts are being received at the unlicenced address. The simple absence of a licence does not constitute this, nor does the householder's refusal to communicate with TVL/BBC. To obtain a search warrant, TVL/BBC must offer the court positive evidence, such as seeing or hearing a television, or the householder's own admission. Without such evidence, TVL/BBC cannot apply for a search warrant, and without a search warrant, they cannot enter. So, they are back to square .