There was no warning from the pump. No noises, knocking etc just a sqeeeeeeeel very closely followed by a bang as everything went pear-shaped.
It's trashed multiplel valve stems and guides. According to the mechanic I normally use who looked at it first even getting to the head is a nightmare due to the way it's installed - he's not exactly surpised at the repair quote, but did expect Citroen to offer more towards it.
The entry on Honest John actually relates to my car.... I emailed him yesterday. The general feedback is that Citroen are bing a bit tight. The pump shouldn't have failed, but at the end of the day there's no come back, and sh1t happens.
I'm still in discussion with Citroen about trying to get them to up their offer, but I'm not holding my breath.