How long is a very long time, months, years?
It could also be wrapped up in someone's estate (could be years to try and trace relatives and similar or may be none traceable) or a former repossession, company insolvency so now in bona vacantia, so many possibilities.
Someone somewhere owns it and you'd be looking at 12 years before being able to have any chance of a legal claim, that's a long time for someone to come forward or someone else to chance their luck after you've done a load of work.
You don't have a legal right to get them chucked out. You can't see or mortgage it or rent it out.
The Land Registry should give an indication though it could be possible that a change of ownership has not yet been registered.
http://www1.landregistry.gov.uk/