OP
1000deville
Rights to goods until 'sold' is a massive legal minefield and fraught with lots of technical complexities. For starters you need to have EXACTLY the right phrase in your T's & C's for one thing.
For example, say you do a two week long job and quote it at £2k all in. The customer pays you £1k upfront at the start but then doesn't pay at the end - so who now 'owns' 50% of what, exactly? There are ways of safeguarding, but they need expert crafting.
Kate, Rockingit is absolutely right. It is essential that you have what is called a `Reservation of Title' clause included in your terms and conditions of service, and certainly at the bottom of your invoice or on the reverse (include a PTO for Terms & Conditions where necessary). If you only get paid for half a job, then your Reservation of title will be deemed to be on a Quantum Merit (i.e. a 50% proportion of the overall invoice value).
For someone to sue, there has to be in existence a direct contract or an implied direct contract linking the two parties. The aggrieved party also has to show they have suffered a loss as a result of that contract. Alliance FM Ltd are third party facilities managers who act on behalf of landlords. If Alliance FM Ltd contract with you to carry out a repair, you can sue them if they do not pay you. You cannot sue the landlord because he/she has no contract with you. Similarly, if the landlord has an issue with a job you have done, he/she can only seek redress from Alliance FM Ltd, because that is whom they have their contract with. It would then be for Alliance FM Ltd to in turn seek redress from you.
Now, if the landlord has paid Alliance FM Ltd, but Alliance FM have not paid you, then, as long as you have a valid Reservation of Title clause in your Terms & Conditions, you are entitled to claim your goods back (you have to write off any labour value). Unless they can show a loss (difficult if they have not paid you) Alliance FM Ltd are stuck. The only problem with suing a company like Alliance FM Ltd is that it costs money to take someone to court and even if you win, they are still not obliged to pay you. Okay, it means they end up with another CCJ, but as they don't seem to give a d**n, you end up even further out of pocket.