The i6 has been sat for a few weeks as I've been working away. Came to start it and the the battery didnt have enough to fire her up.

Disconnected battery, on charge overnight.

Connected this morning.

Everything works normally, locks and unlocks, wipers, lights, heater, windows, shift lever unlocks, (no she wont start in neutral either). Push the button and nothing, although I have noticed the alarm light is doing a double flash, not sure if that's normal and I've just never noticed.

I've done a hard reset and checked for error codes (none)

Feels immobiliser related to me

Any suggestions? 57 SE i6

Sounds like car has shut down, they can only tolerate about a month of no use. Not sure though how to tickle back to life when this happens. FL2 MY10 TD4 GS traded in at 2 years
FL2 MY13 TD4 GS Current

How old is the Battery? sounds similar to a problem I had once and it turned out the battery had completely died.
Dave DAVE.

Have you got any voltage readings, if a cell has gone it may have enough to power lights but not turn over the engine. 
Hung like Einstein, smart as a horse.

I would say the battery,I would try just for the hell of it unlocking the car with the the key in the fob then trying to start it,if it’s gone into shut down mode it may just help.

Just put a new battery on and no change.

Everything works except when I push the start button nothing happens. It doesnt even try to crank, it obviously goes through a start cycle because after 4-5 the dash reverts to the ignition on appearance. 57 SE i6

Tried opening it with the key, that just tripped the alarm. 57 SE i6

Steering lock ?

http://www.freel2.com/forum/topic32830.html?highlight=start+fuse 
Hung like Einstein, smart as a horse.

Nope, I get everything this guy describes, lights, dash, beep beep of open door but when I push the button I can hear something happening (like a start cycle) but nothing from the starter 57 SE i6

Sounds like a job for mr RAC/AA

Might be worth giving the starter motor a solid tap and if you can a volt meter on the battery when you hit the starter, see how much voltage drop your getting. 
Hung like Einstein, smart as a horse.

The voltage of the new battery? Procrastination, mankind's greatest labour saving device!

Acoustic insulation ARB TPMS 3xARB air compressors After cooler Air tank On-board OCD pressure air/water cleaning Additional 50L fuel Carpet in doors ABE 2x1kg Waeco 28L modified fridge Battery 4x26ah Solar 120w Victron MPPT 100/20 DC-DC 18amps 175amp jumper plug Awning 6x255/60R18

If it's any help, check list from Manual.

The engine does not crank (starter motor does not turn)
Gear selector not in P or N position
Battery Harness/Connectors
Starter motor
Starter relay
Start switch
Transmission control module (TCM)
Engine control module (ECM)
Engine seized
Make sure the gear selector is in the P or N position and correctly adjusted.
Check the battery condition and state of charge.
Check the starter motor and harness.
Check for DTCs and refer to relevant DTC Index


You say no codes are in system, so have you damaged ECM during charge, or somehow lost the code internally which allows the ECM to give permission to start the engine? FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 79k+ miles) (MY2015)
Metro in its 11th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)

Try a jump lead straight to the starter motor check on you tube how to do it. Understeer when you hit the wall with the front of the car.
Oversteer when you hit the wall with the back of the car.
Horsepower how fast you hit the wall.
Torque how far you take the wall with you.

Flashing jump leads around a modern car is not a great idea IMHO. Every chance of shafting your electronics. FL2 MY10 TD4 GS traded in at 2 years
FL2 MY13 TD4 GS Current