Search all clients

My untested guess without looking at your dabase structure would be something like:

SELECT sum(generalinsurance.AmountGI) + sum(protection.amount) + sum(buytolet) + sum(mortgage) + sum(referrals) + sum(overseas) AS total_amt, users.UserID
FROM users JOIN clients on users.UserID = clients.ClientUserID
OUTER JOIN protection on clients.ClientID = protection.clients_ClientID
OUTER JOIN generalinsurance on clients.ClientID = generalinsurance.clients_ClientID
OUTER JOIN buytolet on clients.ClientID = buytolet.clients_ClientID
OUTER JOIN mortgage on clients.ClientID = mortgage.clients_ClientID
OUTER JOIN referrals on clients.ClientID = referrals.clients_ClientID
OUTER JOIN overseas on clients.ClientID = overseas.clients_ClientID
GROUP BY users.UserID