Had a similar problem where I park, I just bought a post and blocked the car in, told the owner to call me and I’ll let them out when I could find the time, as it was my property there was nothing they could do. I kept them in for 3 days 
Its illegal to clamp a car if there are no signs warning of a clamping. I think installing a post (like I did) would be a better solution.
I would get the company who sold the space to you to install one of those locking bollard things that fold up and prevent unauthorised use of the space. They are not that expensive and without it you have probably wasted your money buying a space you can’t even use.
One like this:
http://www.heald.uk.com/shop.htm?product_group=11&product_id=7
Could make a sign up in less than a minute 
I can’t remember who i was talking to but I remember someone telling me they had a problem with a persistent rogue parker. After leaving a few polite notes on the car to no effect, they then plastered the whole glassed area with notes… Araldited to the glass:D:D:D
Go quickly print off a warning that you will be clamping anyone in the car park who doesn’t show a badge, make it nice print and laminate it, print off a car badge for you. Make sure they look good, make sure you write down that a fee of £125 will be charged for declamping. Clamp his car, take photos and that’s that.
Or move his car in the middle of the road, call the police/council tell them a vehicle is obstructing the road.
I asked the same question a while ago and got some interesting answer, one was from our lovely John with what can and cannot be done based on UK Law, might suggest doing a search for it. The owners did a sign and used a parking company to remove it, they didn’t have to pay anything since they make the money by removing the cars, they charged £425 to release teh card.
There is no law about 2 weeks, that’s just the company not wanting to deal with it, they probably know whos car it is:)
the owner can come take the car on the 13th day go for a drive come back and park it again for another 13 days:)
So you have the coices stated:
1)Make a sign and clamp his car and charge them a release fee of £125. Or tow the car away and charge them £425 for release. Make sure the fess are stated on the sign, a phone number should be on there also.
2)Stick paper with a warning that he is parked in your spot, make sure you use superglue, locktite or something strong, it will be a bitch to remove.
3)Get in touch with the towing company ask them what they are playing at, there is no 2 weeks law, tell them you will be going to a different company which deal within 24 hours. Check around and call other parking companies see if they are willing to stick a sign up and tow/clamp any idiots that park in your spot.
4) Use a biker balaclava, block the CCTV so they can’t film **** and remove the car, leave it in middle of the road and get someone to call police/council to remove it (don’t do it since you live there and can be linked to you). Or simply vandalise his car. There is nothing they can do since there are no witnesses and most important no 3rd party witness.
5) If you know who the person is wait for them in your car and run them over, claim you sneazed or the sun glared or whatever blusshit you want and get away with murder:) (disclaimer this is a joke linked to a previous thread, I seriously hope you won’t kill anyone)
i had a similar problem! someone parked in front of my garage so i couldn’t park or put my car in the garage! so i parked my car behind the other car i went to the ace on my bike!! when i came back the guy was really angry!! i told them next time he would find his car on top of 4 bricks!!:w00t:
Unfortunately, these days you have to have a SIA licence to clamp vehicles on private land - otherwise you’ll be in the thick and smelly.
Better off just threatening violence (I’m sure a few of us ‘big’ lads wouldn’t mind coming along for effect 
)
I don’t think you do mate, only need that to get details for registered keeper from DVLA. Anyhow I might be wrong but from what I’ve researched for my friend you don’t need a license. It is your private land, you have sign posted informing them of their action and that’s that. By going against the sign they are accepting full responsability which is a contract… or so to speak. So you say, “anyone parking in my parking space which is owned by myself and no one else will get clamped and a release fee of £125 will have to be paid to release the clamp” they park anyway and by doing so they accepted the statement, hence accepting the contract hence getting clamped.
Find out where they live and drag the f*cker by the earlobes back to the car, so they can see the error of their ways.
But maybe an easier way would be to see if it’s in gear or automatic. If neither, you might be able to cut the handbrake cable from underneath, and let it roll out of the space. May require a bit of shove.
I got the big 4x4, you got the chain??? Lets do it:w00t:
Just found the above on the SIA website - looks like you have to be licensed - i think i read in there somewhere, it only applies if your CHARGING a release fee.