All good points you all have raised.
It's impossible to know where the bottom is when the market is this volatile.
The FTSE100 is now down 39% from the all time highs (inflation adjusted). I did not consider it particularly expensive when it was trading near it's highs, so I consider it a generational bargain where it is right now. But that is not to say that it can't get cheaper! It can always get cheaper in a bear market, just as it can always get more expensive during a bull market.
The fly in the ointment, as I see it, is that US markets are still not particularly cheap. The Dow has little technical support until 18,000, so we could easily drop another 15%.
In any case, it's crucial to have a plan of attack. Having now emptied all my bullets at this thing, my plan is that if we see FTSE 4700 I will swap 1/3 of my bonds for the FTSE, then @4400 another 1/3rd, and 4100 the last 3rd, and all the time I will be a regular buyer over the next few years anyway with every paycheque.