Can i bypass my immobiliser on a rexton 290 2005 as the key fob is just flashing but the doors will not open and the car will not start.

If you can bear the alarm - defender are recommended here open the drivers door with the key - alarms will go off , open the bonnet & take off battery for about a minute - the alarms will still be going -& in the engine area VERY loud - reconnect the battery.
with new battery in the key fob press & hold both buttons near to the steering column, and there is a tiny red led - once this is on press the door open button, and close it - repeat twice & it should all become quiet and your key will now work - reset the second fob pressing both buttons.... otherwise there is a cable clip ( white - 3 inches long by 1/2 inch wide with 15 cables going into it ) - behind the steering column, 2 side by side arrays of cable clip-in units going into the engine management unit & alarm system ~ remove the white clip - should disable the sensors but it knocks out other system & fog lights etc - should get you to a dealer to get fixed - ( thank you SSangyong dealer in Cognac France who showed me this trick)

Change the batteries of the key fob

or chnage the car battery