Looked in spare wheel section of boot today, found a yellow plastic thing straped into boot of car it says diesel on it ,any ideas anyone

To reset in case you use wrong fuel;

Reset the misfuel protection device as follows:
1. Insert the reset tool (with the teeth
uppermost) as far as it will go into the filler
neck.
2. Locate the teeth by pushing down the top
of the reset tool.
3. WIth the top of the tool pressed down and
the teeth engaged, slowly pull the tool out
of the filler neck to reset the device.
Do not twist the device, once the teeth
have engaged.
Note: The yellow part of the protection device
should no longer be visible in the filler neck.
Return the reset tool to the luggage
compartment.

didnt have one on my other freelander

Hopefully LR took on board the number of misfuels in previous models to fit this simple device and avoid serious engine damage.

In previous cars I'd bought the filler cap thingy from dragons den

It is still possible to put the wrong fuel into the vehicle even when the misfuel device is activated but it is a very slow process. With the misfuel device activated the trigger on the fuel nozzle will constantly trip out and to put fuel in you will have to constantly pull and release the trigger and that will hopefully cause you to check which fuel nozzle you are using.
Once I had to filll a Discovery with the misfuel device activated, someone had misplaced the reset device and it took about 20 minutes to put £50 worth of diesel into the vehicle.

Very annoying when trying to reset and the yellow plastic thingy breaks! With no LR dealer in town, life is hell filling the FL2 up now. Any tips for broken thingys"