Allotments 4 All

Gorilla Super Glue.  http://www.gorillaglue.com/glues/superglue/index.aspx

It expands slightly and sticks hard plastic very well.

They do other types of glue too, but I haven't tried them yet.

Where can you buy it?

Most DIY places have it or you can buy it online from sites like.
http://www.gluegorilla.co.uk
http://www.gorillaglueonline.co.uk