[Potty Plotty Lotty]

Or it's marginally cheaper at Toolstation @ £27.48 if there's one near/closer to you

http://www.toolstation.com/shop/Plumbing/MDPE/MDPE+Pipe+25mm+x+50m/d20/sd2729/p50903

[Fen]

Don't make the mistake that I did. Used black alkathene? water pipe. Cut in into 5 ft lengths. Put in sticks either side of the row, pushed on the pipe ends and as soon as it got warm it flopped and was absolutely useless. Use the blue water piope as recommended.