“[Samuel Whitbbread] spent the evening of 5 July  in frenzied discussion of the finances of Drury Lane with his solicitor, and on the morning of the 6th, after a badly disturbed night, killed himself by cutting his throat.
The surviving evidence seems to suggest that while Whitbread retained his sanity until the moment he took his own life, he suffered from a severe physical disorder of the brain which, with the immense exertion required to fulfil his manifold commitments, destroyed his metabolism and deeply disturbed his mind. As a result, he began to exaggerate his financial problems and became increasingly prone to unreasonable agitation over trifles. Whether he was driven to suicide by a sense of guilt over the failure of the Drury Lane venture to realize the expectations of the investors, or by a paranoiac belief that the fall of Buonaparte symbolized the failure of his own career, must remain a matter for speculation.
Both friends and opponents acknowledged his outstanding qualities of honesty, courage and humanity. He had, in the words of Lord Glenbervie, a ‘powerful coarse intellect’ and, as Holland noted, an ‘extraordinary readiness and indefatigable application in business’. The remarkable range of the interests and causes which he espoused prompted Sir Robert Heron to judge that ‘few men have been so extensively useful to the country’. His passionate oratory and fearlessness in debate made him one of the half-dozen dominant figures in the House after 1807. Williams Wynn wrote that when he got hold of ‘the right nail’ he ‘drove it with a sledge-hammer, in a manner which no other man in the House of Commons could reach’. But there was an unfinished quality about Whitbread, whose coarseness more often than not intruded into his speeches. Byron called him ‘the Demosthenes of bad taste and vulgar vehemence, but strong, and English’, and William Wilberforce recalled that ‘he spoke as if he had a pot of porter at his lips and all his words came through it’.
More serious defects in Whitbread as a politician were vanity, arrogance, lack of judgment and wilfulness. Holland wrote that ‘vanity made him impracticable’ and that ‘flatterers and dependants engrossed his society, and not infrequently perverted his manners and judgment’. Williams Wynn commented:
I have seen him repeatedly quit a strong question which he could have urged with great power to run after some tub which had been purposely thrown out for him by his adversaries, and which he struck at totally without effect.
Heron’s observations on the same theme were:
In Parliament, his bad taste, and, what is perhaps the same thing, want of judgment: above all, his impracticable disposition, and total want of co-operation, diminished greatly the advantages which might otherwise have been derived from his great ability as an orator, his experience, and his incorruptible firmness.
Romilly was more charitable and thought that ‘the only faults he had proceeded from an excess of his virtues’.
Whitbread’s career ended in political failure and personal tragedy. It might have been otherwise had he obtained office with the ‘Talents’, though this can hardly be taken for granted. By 1808 the breach which had been opened between him and Grey was being inexorably widened by the intrusion of basic differences in their political attitudes. Whitbread’s personal disappointment and political extremism became mutually sustaining. It would be unfair to question the sincerity of his espousal of reform, even more so that of his campaign for peace; but his motives were complex, his emotions tangled, his ties with orthodox Whiggism too close to be severed completely and his ambitions for office still keen. Consequently, his extremism was fitful, erratic and often equivocal and his radical potential was never fully realized. He might well have been able to make a valuable contribution to the development of the Whig party, but such opportunities as occurred after 1808 to re-establish a durable working relationship were lost as a result of his own wilfulness, his jealous resentment of Grey, his susceptibility to the flattery of the mischievous and largely insignificant men with whom he surrounded himself and, not least, Grey’s failure to assert his authority over Whitbread, whose waywardness was a symptom as much as a cause of the disarray of opposition in this period.
As a parliamentarian, he certainly made his mark. Holland wrote at the time of his suicide that
it is no slight homage to his character that at a moment when the grief of everybody seemed to be engrossed by some loss in the battle of Waterloo, his death should have made so deep and so general an impression. Truth is that, with all his failings—and some he had—he was not only an able and honest, but a most useful public man.
Wilberforce commented that Whitbread, ‘with all his coarseness, had an Anglicism about him, that rendered him a valuable ingredient in a British House of Commons’.”
— “WHITBREAD, Samuel II (1764-1815), of Southill, Beds” by David R. Fisher. Published in The History of Parliament: the House of Commons 1790-1820, ed. R. Thorne, 1986