I would guess that you're in the UK since all your links are .co.uk. This forum is mainly US based so most here are not familiar with your stuff.
What you need is someone familiar with X10 for your control applications and someone familiar with UK locking mechanisms. Luckily we know someone who fits the bill
The alleged electric mortice lock that you're looking at is not an electric mortice lock - it's an electric strike. The correct operation electrically is that the solenoid releases the lock mechanism when voltage is applied directly to the terminals. The way you're describing the operation is exactly as I would expect. You need to install your universal module to operate as a switch to your power supply as described by NYbuck (who did an excellent job). The universal module does not actually output 24v DC at 5 amps, it is merely rated as a switching device that is rated to carry up to 24v DC at 5 amps.
The problem you're having is that the lock you are using is probably not compatible. The usual definition for a UK mortice lock is one that is locked and unlocked with a key with no slam-shut action. The description on your electric strike is very misleading - it says for mortice locks, but then says it is for Yale type locks. Most Yale type slam-shut locks are not morticed into the edge of the door, and most mortice locks in the UK are not slam-shut.
If you're trying to electrically unlock a conventional UK style mortice DEADlock, such as a Chubb 3G114 or similar, you need an entirely different and much more expensive electrically released strike especially designed for deadlocks.
Although when you're bench testing this system you will need to apply a degree of force to the strike to make is operate, this force is very much diluted when you have the 'sail plane' of a 6 foot x 3 foot door doing a lot of the work for you.
Next problem...
The spec on your strike says 12v DC, 12v AC and 24v DC - this is very unusual. Electric strikes in the UK are normally rated 5-8v AC, 12v DC, 12v AC or 24v DC. Something that tries to cover both 12 and 24 volts without having some kind of voltage change for the solenoid is likely to suffer from major failure fairly soon when the solenoid burns out from overvoltage. On closer inspection of the really poor image available, the electric strike can only really be described as 'complete and utter pants' - probably manufactured in China under license from Spain with some Korean parts that were bent up out of rusted out Toyotas. Cheap and cheerful is a phrase that springs to mind, with the emphasis on cheap and the cheerful part crossed out and replaced with the word nasty. I seem to remember these things retailing for about 12 quid with a wholesale price of about 3, but that was about 6 years ago. By comparison, a half-decent electric strike was retailing for about 60 notes and a really good one closer to about half a monkey - I should be getting commission from Google on their English slang searches
Next problem...
X10 only has 256 theoretical codes available - I won't go into the where's and why's of what codes shouldn't be used as there is plenty of information out there on that. In practice you will be securing your door with a worse than 1 in 250 chance of someone chancing on your code if they know that you're using X10; this is not fantastic security, most X10 users can scan through all available codes in just a few minutes and therefore have your door open in just a few minutes.
Next problem...
Most people are unable to close doors after they walk through them. You should probably also look into installing a door closer to make to door self-closing so that your minimal security via X10 is active as much as possible. A door that has been left ajar is now down to zero possible codes to allow someone to walk through.
If you could let me know the make and model (or take a picture or three) of the mortice lock you're trying to use, I can probably help with specifying the parts you'll actually need to control your door if you still decide that the convenience of an electrically unlocked door is worth the substantial decrease in security that you'll see.
The important thing to remember is that electrically unlocking a door is usually a convenience that severely affects your security. Your insurance will most likely be voided if you have a break-in via a door that is electronically locked and unlocked - you should check with your insurance people before you go ahead with installing anything like this on an external door.