UK is to be considered as an Associated Country to Horizon Europe in the frame of PF and DN calls.
For PF: a fellow who plans to be hosted by an institution located in the UK must apply for a European PF.
For DN: partners located in UK can be beneficiaries and the doctoral candidate(s) recruited by UK partners are taken into account in the count of person-months funded by the EC (max. 360 or 540 person-months depending on the DN mode).
If the HE Association Agreement between UK and EC is not signed by the signature of the PF 2022/ DN 2022 Grant Agreements, successful UK applicants will receive funding from UKRI. Currently, the UK government guarantee only covers those eligible calls where the grant agreement needs to be signed by 31 December 2022.
More info can be found at https://www.ukri.org/apply-for-funding/horizon-europe/