I suspect this is a classic Lib Dem trick I've seen elsewhere - they will pretend it is some sort of important, official survey but actually it is just a way for them to gather information about you/your voting intentions/what issues you find important. Once had one sent to me by post saying "(Your Area) Residents' Survey" followed by questions on every topic you can imagine, then in tiny letters at the bottom "Printed & Promoted by the Liberal Democrats" (which they are legally obliged to put on all election material).