I need to plug an extension into an extension.

I have bought some lights for the top of a book case. The book case is tall, the leads are short. So an extension will go behind the book case, but the only socket left is into another extension. Now I have a double socket behind the bookcase going into a 4 socket. The 4 socket has only two plugs going into it, so that leaves two spare sockets. I figure that the 4 socket was made for 4 sockets, so a double socket takes up two sockets which is the same as the 4 socket being filled to capacity. But I'm just guessing, so is that right?

4 - 2 = 2

2 + 2 = 4

It's the same thing right?

If you are concerned about overloading the electrical capacity of the extension then I can reassure you there won't be a problem with only lighting connected. 

Take care with the way you support the extension blocks so that there is not continual strain on the leads to the plugs.

Do not however double up extensions with any high power consumption equipment such as a heater or kettle. In fact it's best not to use extensions with high power appliances at all..

OK Thanks! The extension lead is quite light, should be OK.