Of course there will be further attacks. It's nothing short of a miracle that none had been successful in the UK since 2005 anyway.
HOWEVER, that 23000 will include all those whose names have come up in investigations, even erroneously (there was a thread the other day from a poster who had a call from social services after police had identified her daughter in connection with something - turned out to be police error and a girl with a similar name: this happens in counter-terror also, unsurprisingly, given the very small pool of common names etc)
There's also those who are overt sympathisers (but wouldn't do it themselves) known to the police, those with broad sympathy who've come to police notice for other things, and those who would like to carry out an attack and actively pursue it.
I've seen various estimates that the latter (in Europe, not just in the UK) are somewhere between 1% and 3% of the total figure of those known.
So in this instance, of the 23k. HOWEVER, it doesn't end there. In order to get as far as carrying out an attack, you don't just need someone with a motive, but also with a) the means (whittles down the pool even further) and b) the opportunity (ditto)
HOWEVER, even though there's a tiny proportion who fulfil these criteria, the number of potential attackers gets even smaller - because of informing, surveillance, police work etc etc So 23k is a scare-mongering figure with little real meaning except when used to create moral panic.
All that said, the terrorists only have to be lucky once to succeed - security services have to be lucky every time.
Blaming this - or 7/7, or 9/11, or any other terror attacks on any government is naive at best, and ignorant politicking at worst.