He opposed the compelling of Protestant Nonconformists to take the oath required of Roman Catholics.
To the north of the village, which has extended greatly as a residential suburb of the metropolis, is Mill Hill, with a Roman Catholic Missionary College, opened in 1871, with branches at Rosendaal, Holland and Brixen, Austria, and a preparatory school at Freshfield near Liverpool; and a large grammar school founded by Nonconformists in 1807.
Complete toleration in fact was only extended to Protestant nonconformists, who composed the Cromwellian established church, and who now meted out to their antagonists the same treatment which they themselves were later to receive under the Clarendon Code of Charles II.
As it was, although Parker said that Grindal "was not resolute and severe enough for the government of London," his attempts to enforce the use of the surplice evoked angry protests, especially in 1565, when considerable numbers of the nonconformists were suspended; and Grindal of his own motion denounced Cartwright to the Council in 1570.
In 1674 he is mentioned as endeavouring to prevent the justices putting into force the laws against the Roman Catholics and Nonconformists.'