Sentence:  ‘Regrettably, I have concluded, after considering the matter over Christmasnb..., that I can no longer maintain the high standard of service I <WSD>require</WSD> of myself, meet the demands of office and cope with the pressures of public life, without my health deteriorating further.' 
Meaning of the word marked with <WSD> tags:  To demand, to insist upon (having); to call for authoritatively. (from 14thc.)