How would your garden grow if you grabbed that patch of wasteland?

So there's this derelict patch on the other side of your fence. Could you stake a claim? By Kathleen Hennessy

Space is a little like time: we could all use some more of it. And what home-owner wouldn't jump at the chance to add a few extra metres to their garden? Several websites – www.land4free.co.uk, claim-free-land.co.uk and landclaims.co.uk – declare that acres of unused space are just waiting to be snapped up, but can you really claim any of it?

According to the Land Registry, about 65 per cent of the land in England and Wales is registered freehold – but that doesn't mean the other 35 per cent is up for grabs, says Marion Shelley, spokeswoman for the registry. "It's a mistake to suggest that just because land is unregistered, nobody owns it. All land is owned by somebody, whether an individual, a company, the Government or the Crown."

But let's say there's a strip of land adjoining your back garden that you feel would make a nice addition to your property; there's nothing built on it and it's never been used by anyone for anything. Can you take it?

"First you need to find out if it is registered," says Ms Shelley. You can do this at www.landregisteronline.gov.uk by using a map and aerial photograph system to locate the site. You will then need a plan of the location to send to one of the Land Registry's local offices.

If you can't achieve any clarity this way, says Ms Shelley, then other possible leads are the owners of neighbouring homes and the empty properties officer at your local council.

Assuming you draw a blank, you can try to acquire the site through "adverse possession". This involves occupying and using the land, to the exclusion of all others, for a long period – 12 years if it's unregistered, though some land owned by the Crown must be occupied for at least 60 years before you can claim title.

"A lot of people misconstrue adverse possession," says Richard Hegarty, a senior partner at solicitors Hegarty. "If you are in possession of the land but with the owner's permission or knowledge, that's not adverse possession."

Nor can you claim a piece of land just because you always mow the grass on it. If others use the same plot or there's a right of way across it, you can't claim exclusive use. "You really have to physically exclude everyone else," says Mr Hegarty. "We have one dispute at the moment where the claimant has been in adverse possession for over 20 years and has fenced off the land. But the Land Registry is arguing that, as one of the boundaries is a river, the land doesn't really exclude all others. Presumably, they are supposed to access the land by canoe."

If you do think you can stake a claim, you must register it by supplying a statutory declaration that will detail when you started adverse possession of the land and how the site is being used. This has to be sent to the Land Registry with an Ordnance Survey plan of the site – which can be downloaded at www.ordnance-survey.co.uk – and a statement of the land's value, which you have to determine yourself. Fees are based on this value and are on a sliding scale from £525 to £30. If the Land Registry carries out a site inspection to double-check your valuation, there may be a further £40 fee.

At this point, the legal owner has a further two years in which to object.

"After 12 years, you can apply for title," says Mr Hegarty, "but at first the Land Registry is only likely to grant you 'possessory' title. This means you don't actually own the land, but it also means the true owner can't evict you."

It is possible to "sell" the land at this stage, though the possessory title should be underpinned by title insurance as cover against the original owner of the land trying to reclaim it. Title insurance can be bought through a broker.

While most claims for unregistered land are for relatively small areas, they can make a big difference to a property's value by, say, enlarging the garden. In addition, if you were to sell on your claimed land more than two years after the application for possessory title, your buyer would probably be able to gain absolute title to the land.

"And once title is absolute, the legal owner can no longer challenge it," says Mr Hegarty, "unless he can prove some falsity in your statutory declaration – such as you not having exclusive use of the land."