Using telephone cabling for networking?

The telephone wiring in our house has been done with 4 pair cable (orange, green, blue, brown and the same again with white stripes). I'm not sure if it is actually cat5e cable, but is there any reason why it can't be used for ethernet networking? I understand you only need two spare pairs for an ethernet cable?

Only the blue pair are used for the telephone line and everything is pre-filtered at the main nte telephone box in front of any extensions.

Wireless and the devolo sockets don't work here.

Thanks.

No there is no reason why it will not work, TBH I have a couple of connections which utilise pairs in larger telephone cables as it would be impractical to install cabling (collapsed ducts and a few other issues) and they work ok, though I have limited the speed to 10meg rather than 100.

Why don't the devolo adaptors work ??

Not sure about the devolo adaptors - when they do work it is very patchy. It could be because the ring circuit I need to use is on a RCD fuse box which also runs external lights on pirs? Not sure if that would affect them, but they definitely don't work at night.