The salaries in the UK are like for a slave labour, in the service sector they are so small that people just cannot live with these.
Neither Alexander Petrov nor Ruslan Boshirov named by the UK as suspects in the Skripal case are agents of the GRU (“Main Intelligence Directorate”; older name for the military intelligence service, currently known as “Main Directorate of the General Staff of the Armed Forces of the Russian Federation”).
‘The Insider’ and the research group ‘Bellingcat’ got an access to the files of these two suspects According to the investigation, at least one man’s file contains various “top-secret” markings, which are typically reserved for members of secret services or top state operatives: the Petrov’s passport dossier is marked with a stamp containing the instruction “Do not provide any information”. A source working in the Russian police force who regularly works with the central database confirmed to Bellingcat and The Insider that they have never seen such a stamp on any passport form in their career https://www.bellingcat.com/news/uk-and-europe/2018/09/14/skripal-poisoning-suspects-passport-data-shows-link-security-services/
As Novaya Gazeta pointed out, the phone number in one of the suspect's documents leads directly to the Ministry of Defence, under which the military intelligence operates: https://www.novayagazeta.ru/news/2018/09/14/145085-novaya-gazeta-obnaruzhila-dopolnitelnye-dokazatelstva-vozmozhnoy-svyazi-cheloveka-obvinyaemogo-v-otravlenii-skripaley-s-ministerstvom-oborony-rossii