My first inclination is to assume that a lens error is the intermittent problem itself, but first, there is a more likely possibility, lack of sufficient power. Remove the battery, check the pins or connectors in the battery compartment, and make sure that they are positioned correctly to contact the battery. Then use a q-tip with alcohol to clean and dry them.
It is also a known issue that digital cameras circuitry can also become much more sensitive to the lower power level produced, so if you have been using the same rechargeable batteries for the life of the camera (more than 3-4 years), yours would be around 4-5, then the power capacity of the battery may not be high enough anymore to handle the increased load. A new battery may be the answer.
Just to clarify, the lens moves in and out noisily when switched on but remains out when switched off. We have tried the suggestions: cleaning the battery contacts, knocking near the USB cover, pressing the lens when camera on its back though the sections do not appear to be out of line. Don't want to go to expense of buying expensive new battery if this is not the problem. This is the 2nd battery in the life of the camera. I don't feel confident in dismantling the camera. Unless you can assist further I think I should send the camera registered post for a free estimate for repair - such repairs come with a 3 month warranty through sendan cameras in London. Do you offer such a service?