However, his Parliamentary activity centered on committees dealing with various aspects of the war with Spain, and he was an open critic of the Duke of Buckingham's conduct.
[1] During the 1630s, he took part in his father's efforts to drain the Great Level, serving as a commissioner of sewers there from 1631 to 1636 or later, but was largely occupied in dealing with his own accumulation of debts.
[1] The lord St. John...got himself well beloved by the reputation of courtesy and civility which he expressed towards all men, that, though his parts of understanding were very ordinary at best, and his course of life licentious and very much depraved, he got credit enough, by engaging the principal gentlemen of Bedfordshire and Hartfordshire to be bound for him, to contract a debt of fifty or threescore thousand pounds; for the payment whereof the fortune of the family was not engaged, nor in his power to engage...he left the kingdom, and fled into France; leaving his vast debt to be paid by his sureties, to the utter ruin of many families, and the notable impairment of others.The figure of £60,000 for his debts was given in a petition to the House of Commons in 1641; an enormous sum, if truthfully reported, for an heir apparent with a negligible estate of his own to offer as security.
Two earlier petitions recited liabilities on his part of £6,900, still very significant, and he was also prosecuted as a surety for the debts of Sir Thomas Cheney, his uncle by marriage.
As Clarendon avers, his debts did cause havoc for his sureties: some of the possessions of his uncle Sir Alexander St John were distrained by Lord St John's creditors, and Sir Capell Bedell, another surety, made a composition with Lord Bolingbroke to pay some of the debts to avoid the same fate.
[1] On 21 November 1638, he obtained a passport to travel for three years under the alias of "St John Thompson", but the deception was discovered, and he was arrested under a warrant from Sir Francis Windebank on 21 December while lying ill at Rye.
[1] His writ was said by Clarendon to have been granted with the object of composing his debts and reducing the turmoil among his sureties in Bedfordshire, and obtaining an adherent of the Royal party in the Lords; but St John showed no attachment to the King's cause.