i am going to buy a sub i want to use it when listening to cds mainley can anyone suggest something up to £300 thanks.

Have a look at the range from BK.

BK-XLS200-DF

http://www.bkelec.com/HiFi/Sub_Woofers/XLS200-DF.htm

Complete range.

http://www.bkelec.com/HiFi/Sub_Woofers.htm