Top UK and European SMB accounting, tax, legal firms

I'm looking to connect with firms experienced in working with SMB owners in the UK and across Europe that ideally provide at least 2 of the 3 service areas: accounting, tax, and legal. Bonus if they do retirement or succession planning. They should have extensive experience on both providing these shared services as well as completing transactions related to search fund entrepreneurs / ETA.

Related to this, I'm curious which accounting system has been most common in the businesses where commercial & FDD has been performed? Quickbooks, Xero, Sage, or other?