riyadh britain saudi arabia sign framework deal military security cooperation saudi state news agency spa say tuesday redouble efforts counter iran gulf region defeat islamic state prime minister theresa may say december britain would invest billion pound 4.05 billion defense gulf arab state next decade seek build traditionally strong tie conservative oil-wealthy monarchies plan departure european union british defence secretary michael fallon discuss military cooperation crown prince mohammed bin salman serve kingdom defense minister deputy prime minister spa report say without provide detail agreement gulf arab state say iran try expand influence arab countries include syria iraq yemen since march 2015 saudi arabia arab ally wag war iran-aligned houthi force seize control much yemen britain close relationship gulf state draw concern human right group include criticism saudi air strike yemen war kill hundreds civilians british military personnel work saudi force britain saudi arabia sign military cooperation deal state media