"On 4 March 2018, former Russian military intelligence officer Sergei Skripal and his daughter Yulia were poisoned in Salisbury, England, with a chemical determined by the Government of the United Kingdom to be a Novichok nerve agent."
Novichok is a nerve agent which began development in the Soviet Union and continued after its collapse into 1993, and Sergei Skripal is former Russian spy turned double agent for the UK. This question assumes that, given how these facts seem to lead perhaps too strongly towards Russia being the culprit, that the UK or an ally of the UK has pulled a False Flag operation in the attempted assassination of Skripal, implicating Russia.
To look into what the UK would stand to gain from this, we need to look at how the UK has responded to this event. The UK and subsequently many of their allies have expelled Russian diplomats as a response to this. This disrupts the spy network of Russia, which is the only objective benefit of the response thus far. Subjectively one could argue that both the attempted assassination itself as well as the expulsion of Russian diplomats constitutes anti-Russian propaganda, as the assassination attempt has been a highly circulated story that has been implying Russia as the culprit, and the expulsion of diplomats is a relatively cost-free way of expressing displeasure with another country. Though whether anti-Russian sentiment is a benefit at all, intended or otherwise, is subject to opinion as nothing tangible is directly gained from it.
It has also been posited that the close proximity of this event to the Russian election in which Putin was expected to retain his presidency was a factor in this event. There are arguments on both sides for this: those claiming that Russia is the likely culprit have stated that Putin's 'strongman' leadership style would benefit from such an event, as it allows Putin to say "Look at how the world is against you, they blame Russia for every wrong. You need a strong leader like me to protect you from the world". An external enemy diverts attention from internal problems. Those claiming Russia is not the culprit have stated that this could have been an effort to discredit Putin among the Russian population in an effort to harm Putin's victory margins in the election.
As to whether the UK has pulled such operations in the past, there is no indication of an assassination of a former spy or false flagging thereof, but a parallel could possibly be drawn between false flag operations by the UK in coordination with the US during the 1953 Iranian Coup d'etat called in the UK "Operation Boot" and in the US "Operation Ajax". This was, however, 75 years ago.
From an outside perspective, the potential costs to the UK of orchestrating the attempted assassination of Skripal and false flagging Russia - including the possibility that the truth behind such an operation could eventually be brought to light - appear far greater than the benefits reaped, but it is technically possible that this is the case.