Each country publishes the Squawks in the AIP ENR 1.6
The UK AIP is on this link
https://www.aurora.nats.co.uk/htmlAI...dex-en-GB.html
2.2.2.1.3 Types:*7000 – VFR conspicuity code: when operating within United Kingdom airspace in accordance with VFR and have not received a specific instruction from ATS concerning the setting of the transponder.
*2000 – IFR conspicuity code: when operating within United Kingdom airspace in accordance with IFR and have not received a specific instruction from ATS concerning the setting of the transponder.