Useful info about SDLT and VAT see this link
https://www.gov.uk/government/publications/revenue-and-customs-brief-11-2020-vat-and-stamp-duty-land-tax-when-existing-leases-between-landlords-and-tenants-are-varied/revenue-and-customs-brief-11-2020-vat-and-stamp-duty-land-tax-when-existing-leases-between-landlords-and-tenants-are-varied