Citroen Berlingo 1.6 hdi will not start with key?

Thank you for that. I do not believe it's the battery. There is only a single click when turning the key. But tomorrow I will try it with jump leads attached, just to rule that possibility out. When I was getting the relay click, I was also getting three beeps. But all the other electrics were working fine. With headlamps on, and hazard lights on, the wiper motor was going okay - usually a sign of a pretty healthy battery. But starter motor was still not even engaging. Strangely enough, got the car towed back to my house today from the garage, and whilst it was being towed, put it into second gear to see if it would start, and it started without hesitation. But will not even attempt it with the key??