Seems to me there could be several sellers. Anyone who bought when the sp was just a couple of pence is sitting on a huge profit and it would be very surprising if at least some of them were not top slicing. Nothing to do with the placing shares at all - total red herring.
Ethio what is the matter with you ? You have been told many times that you can't just look at the 'buy' and 'sell' categorisation and believe them. 22.55 is definitely not a buy and I'm not sure that 22.66 is either. You need to try a dummy buy and sell from time to time to get the true figures.
tinyurl.com/y54mqzlg - it says "Ministers are understood to have made an order for 450,000 of the saliva tests made by Oxford Nanopore Technologies Ltd."
Just had a look at the trades today between 15:00:00 and 15:30:00. There were 42 trades and I'm pretty sure only 8 were sells (it seems 22.55 and under are sells, everything else is a buy). The trade of 22.626 at 16:25:32 could have been a sell I suppose. But even if it was that is only 9 trades out of 42 over a half-hour period - less than 25%. A similar pattern has occurred throughout today so there are a good deal more buys than sells it seems yet the sp remains static.