Hmmm, if you've driven it and it stopped then you might not get away with it so easily.
is the car still 400m from the garage? or did you manage to tow/trailer it away?
you will probably be ok if you can brim it and prime it with diesel and or diesel/unleaded mix.
If it was me in this situation and I had the time and resources (I have a mobile mechanic brother so this is within scope for me, but might not be for you?)
remove the fuel filter, drain and refit. Put roughly the same amount of diesel in as you have petrol. turn over engine (or just turn on ignition if that primes the fuel filter) to refill fuel filter, remove fuel filter and drain. turn over engine again until fuel filter is full again (this should have the effect of removing the neat unleaded from the lines) crack open (loosen) one of the injector pipes so that fuel pump pressure ****es fuel out of the pipe, to remove the last bits of neat unleaded from the system, retighten the injector pipe and try to start the car,
This should at least get the engine running again.
you can them make up your own mind as to whether to put more diesel in yet (I would)
Run the car and decide later if the unleaded has caused any lasting damage (It might have screwed your fuel pump but I doubt it)
If this sounds like a lot of work/time/effort or you simply don;t have the resources to do it then in this instance I would get a garage/AA/RAC to do it and take the £180+fuel price hit.
It's a shame as all they will do is very similar to the above (but they won;t leave a petrol diesel mix in the tank or lines) and it'll cost you, but having driven it and it stopping it's not as simple as topping up and driving off.