As others have stated, the law expects you to check that anyone driving your car has valid insurance.
The penalties for anyone failing to ensure that the driver of their car has valid insurance are exactly the same as for the driver. The maximum fine is �5000. (In practice, fines are generally much lower than this and also income related. Expect a fine of around �200, plus perhaps �70 costs plus �15 victim compensation scheme payment). In addition the court will endorse your licence with between 6 to 8 points. (In practice it will almost certainly be 6 points).
Chris