Help please !!!!

hi all I have a 95 D1 300 tdi manual

left work today about 3, nice hot day quite warm in the olid girl, put the key in ignition , turned key to pre heat light, then turned key to turn over but didn't turn over and I got a loud click from under the passanger footwell area ?????? every time I turn key in to 'turn over' position I just get a loud click from under the passanger footwell ???

help appreciated ment to be doing a 400 mile round trip holiday next week

Immobiliser issues? I had this but it was a few clicks not just one loud click. I also had issues when i had a poor negative battery conection that was an easy fix remove lead clean up and back on.

I had a fiddle of the 3 relays I could see and in the end a hefty tap on the black box with 2 main plugs on to the bottom of it on the passanger side footwell wall did the trick but this is the second time in a matter of days now so not sure

Where bouts are you someone may halp you
If it was immobiliser issue then it wouldnt click and youd have the key and car red light on dash.

Clicking is usually bqttery so start there.it may be losing power and not enough to crank it.but click is the starter solenoid

I had something similar last night when I unlocked the passenger door first. Assuming it was the immobiliser I locked the drivers door, unlocked the drivers door and then it would start.

Sounds like a battery problem to me. Check the state of charge. Clean both terminals and earth straps. Is the alternator working properly? Another thing to try is running a separate earth strap from the engine block to the battery.
Clicking sounds like the starter solenoid - another set of connections to clean and re-fix.