I'm not familiar with the Brimstone missile but it sure has a descriptive name.
Anti-tank missile, uses the Hellfire parts as 'muscle', and British-made millimetric-wave radar as 'brain'. Using it as an ground-based anti-ship missile is doubious unless the enemy ship closes under 8+- km close to the launcher.
Brtitish (and/or other countries') shipment of Exocets or Harpoons would've been a far greater threat to the Russian ships.