Condensation help please, any tips?

Having real trouble at the moment with condensation and wondered if any of you have any tips for stopping it. I have the pots you can buy from DIY shops on window sills to capture the moisture but they don't work so was thinking about buying a dehumidifier......
anyone use one of these and can recommend a good one? They are quite expensive so don't want to buy if they are not very effective.

Any ideas appreciated.......

Are you air bricks or vents covered ??

It depends on what's causing it, for us when we're cooking in the kitchen the warm air from the kitchen and cooler air from the conservatory meet causing the windows in the conservatory to mist up, so we either put the heating on in the conservatory or put the dehumidifier out there on for a bit until it's dealt with. Usually the answer is to warm the area up but I bought my dehumidifier from
http://www.dry-it-out.com/dehumidifiers
it's very effective and quiet but not cheap, I have a mitsubishi it cost about £300