Thanks for all the replies - very useful.
It is of course correct that the battery should easily withstand one week without use. However, as I probably should have explained, this pattern of infrequent use sometimes goes on for extended periods. Yes, the battery is OK after one week of standing, and two and three etc, but the use of the car in between is apparently insufficient to replace the charge used by the starter motor and through parasitic drain. The result is that, eventually, the car will not start. The problem is essentially a cumulative one arising from low levels of use. I drive around 4,000 miles per year - mostly on country roads.
I have experienced the same problem with previous cars, even replacing the battery only to find the same difficulty returning after a few months. I have previously completely solved the problem by leaving the battery on trickle charge all the time - hence the desire to find a very convenient solution for attaching the leads.
Five years ago I took my previous car for its MOT, and was told that the battery was "unserviceable". I did not believe this because it was a good quality battery for which I had paid a premium price, and it was only two years old! That was when I decided to use a trickle charger all the time. The same "unserviceable" battery was still serving perfectly four years later when I disposed of the car.
I am grateful for all the comments. Thanks and best wishes.