The multmeter shows the cap is charging / discharging. I've checked the circuit several times & the 555 just keeps getting hot, so I guess it's well & truly cooked.
I have the relay protection the correct way around, anode to negative & cathode connected to pin3. The other diode is connected with the anode connected to pin2 & cathode to positive. I have also added the additional diode that you mentioned on pin3 anode to pin3 cathode to relay & the cathode of the first diode I mentioned.
The input voltage is from the cigarette lighter in the car, but I have been testing the last 2 circuit revisions with a PP3 9v battery.
Im using a 5k6 resistor, but the delay isn't too important, somewhere between 5-10 seconds is fine.
I'm going to reorder the parts from maplin & start from scratch.
I have posted the list of components here, can you confirm all the parts are correct.
Cheers!