B6 hot starting

[bigpassat06]

I have a 2006 Passat Estate 2.0l diesel.
From cold it starts first time, every time, and runs perfectly.
Once the engine is up to temperature and I stop somewhere it is really hard to start the car again while it is still hot. When I depress the key the engine will judder but not start, the whole car judders for just a second, like the engine is trying to start, but it will not start.
After several tries, 11 attempts today, it starts and runs very smoothly.
No error or fault messages on the screen.
Can anyone explain the issue? I am not technically minded so please keep it simple. I am hoping it is an easy and cheap fix.
Once the car is cold again it starts fine.
Could it possibly the battery is not supplying enough current to start it??

Many thanks