In 1658 William Brereton 3rd Baron Brereton (age 26) was elected MP Newton.

Evelyn's Diary. 15 Sep 1659. Came to see me Mr. Brereton (age 28), a very learned gentleman, son to my [his father] Lord Brereton (age 48), with his wife and divers other ladies. Also, Henry Howard of Norfolk (age 31), since Duke of Norfolk.

In 1660 William Brereton 3rd Baron Brereton (age 28) was elected MP Bossiney.

Evelyn's Diary. 08 Jul 1667. My Lord Brereton (age 36) and others dined at my house, where I showed them proof of my new fuel, which was very glowing, and without smoke or ill smell.

Pepy's Diary. 12 Dec 1667. Thence walked to my bookseller's, and there he did give me a list of the twenty who were nominated for the Commission in Parliament for the Accounts: and it is strange that of the twenty the Parliament could not think fit to choose their nine, but were fain to add three that were not in the list of the twenty, they being many of them factious people and ringleaders in the late troubles; so that Sir John Talbott did fly out and was very hot in the business of Wildman's being named, and took notice how he was entertained in the bosom of the Duke of Buckingham (age 39), a Privy-counsellor; and that it was fit to be observed by the House, and punished. The men that I know of the nine I like very well; that is, Mr. Pierrepont (age 59), Lord Brereton (age 36), and Sir William Turner (age 52); and I do think the rest are so, too; but such as will not be able to do this business as it ought to be, to do any good with. Here I did also see their votes against my Lord Chiefe Justice Keeling (age 60), that his proceedings were illegal, and that he was a contemner of Magna Charta (the great preserver of our lives, freedoms, and properties) and an introduction to arbitrary government; which is very high language, and of the same sound with that in the year 1640. I home, and there wrote my letters, and so to supper and to bed. This day my Chancellor's (age 58) letter was burned at the 'Change [Map].'

Pepy's Diary. 05 Jan 1668. Thence after dinner away with Sir G. Carteret (age 58) to White Hall, setting down my Lord Brereton (age 36) at my Lord Brouncker's (age 48), and there up and down the house, and on the Queen's (age 29) side, to see the ladies, and there saw the Duchesse of York (age 30), whom few pay the respect they used, I think, to her; but she bears all out, with a very great deal of greatness; that is the truth of it. And so, it growing night, I away home by coach, and there set my wife to read, and then comes Pelling, and he and I to sing a little, and then sup and so to bed.

Pepy's Diary. 05 Jan 1668. After dinner, my Lord Brereton (age 36) very gentilely went to the organ, and played a verse very handsomely.

Pepy's Diary. 05 Jan 1668. From the Vice-Chamberlain (age 58) up and down the house till Chapel done, and then did speak with several that I had a mind to, and so intending to go home, my Baroness Carteret (age 66) saw and called me out of her window, and so would have me home with her to Lincoln's Inn Fields to dinner, and there we met with my Lord Brereton (age 36), and several other strangers, to dine there; and I find him a very sober and serious, able man, and was in discourse too hard for the Bishop of Chester, who dined there; and who, above all books lately wrote, commending the matter and style of a late book, called "The Causes of the Decay of Piety", I do resolve at his great commendation to buy it. Here dined also Sir Philip Howard (age 37), a Barkeshire Howard, whom I did once hear swear publickly and loud in the Matted Gallery that he had not been at a wench in so long a time. He did take occasion to tell me at the table that I have got great ground in the Parliament, by my ready answers to all that was asked me there about the business of Chatham, Kent [Map], and they would never let me be out of employment, of which I made little; but was glad to hear him, as well as others, say it. And he did say also, relating to Commissioner Pett (age 57), that he did not think that he was guilty of anything like a fault, that he was either able or concerned to amend, but only the not carrying up of the ships higher, he meant; but he said, three or four miles lower down, to Rochester, Kent [Map] Bridge, which is a strange piece of ignorance in a Member of Parliament at such a time as this, and after so many examinations in the house of this business; and did boldly declare that he did think the fault to lie in my Lord Middleton (age 60), who had the power of the place, to secure the boats that were made ready by Pett, and to do anything that he thought fit, and was much, though not altogether in the right, for Spragg, that commanded the river, ought rather to be charged with the want of the boats and the placing of them.