Until someone who knows more about elans gives you the proper answer, i can only comment on my thoughts, and how i have solved similar issues.
On my Dolomite, this is a regular occurrence. If the car is damp when it's put away (or even cold!) then there is enough moisture in the clutch plate to enable rust to form, holding it stuck onto the flywheel.
If you have an assistant handy, you can check that the clutch is moving by watching the arm on the gearbox whilst the assistant presses the pedal. When it is held fully down, see if the arm will move any further by pushing it directly, under the bonnet.
If the arm moves with the foot pedal (hopefully full travel) then its looking like a clutch plate stuck to the flywheel.
There are varioyus techniques for freeing them off, ranging from mild to wild!
Firstly, always run the engine until HOT and the fans cut in - that will ensure that some heat has got into the clutch itself (bear in mind that if the car has been standing for a long time, there could be coolent problems aswell

) Don't allow it to overheat - keep an eye on the guage in case the fans are playing up (Don't you just love Lotus electrics!!!!)
Mildest way to start is:-
Turn off engine, engage fourth gear (with nothing in front of the car!), press down the brake pedal with right foot, clutch pedal with left foot and turn ignition key. The theory is that the engine will try and turn on the starter motor, the brakes will hold the car stationary and the rust holding the clutch to the flywheel will break free, alowing the engine to turn / fire, and all gears to engage fully operationally

.
If the clutch doesn't free off after a few goes at this, it may be worth upping the ante.
Jack up the front of the car so both wheels are clear of the ground. place axle stands under the car and lower the jack. apply handbrake and CHOCK THE BACK WHEELS. (all in case the car falls!)
Try the same technique as in method one.
If this fails, whilst the car is in the air, put into third gear, start engine normally KEEP EVERYTHING/EVERYBODY CLEAR OF MOVING WHEELS! Put your foot on the clutch and gently apply foot brake, this may enable the rust seal to break. (if not, the car will stall and we have a few goes, each time adjusting the ferocity with which we apply the brakes).
If you get to the stage where its like an 'emergency stop' and the car just stalls without freeing, its time to get more brutal!
For this, you need a private road / track (I'd never advocate using public roads for this

)
With nothing in front of the car, depress clutch, select 1st gear, turn engine on (having allowed a few seconds with key in possition 1 to reset the electrics etc). the car will lurch forward and as the engine fires, it will drive away. Maybe the clutch will free up with this, if not, as the engine speed increases, change gears (hopefully without too many graunches!) until you are doing about 25 mph in third gear (engine slightly above idle!). keeping your foot on the clutch as you go, hit the brakes (when theres no-one behind you!) and this may jolt it free.
If it still wont work, last stage is to repeat above, but get it into second or third, keep foot on clutch and rev the bol***s off it from 3000 rpm to red line - this may also work!
If none of these things work, you may have to resort to removing the gearbox and manually freeing the plate - but rest assured, i've only had to do that once - the above techniques usually work somewhere along the way!
always try the gentle way first and build up.
always have a fully-charged battery
always do it on a warm engine
remember this next winter, and start the car up every month in the garage, making sure that the clutch doesn't get a chance to rust up!
Good luck!