[1] Reputedly the richest man in Derbyshire, Gell proved an effective and energetic general, but the plundering conducted by his often unpaid troops provoked numerous complaints to Parliament.

According to Puritan diarist Lucy Hutchinson, he "had not understanding to judge the equity of the cause, nor piety, nor holiness", while his men were "the most licentious, ungovernable wretches that belonged to the Parliament".

[5] These included Royalty payments on lead produced from mines near Bakewell, Hope and Tideswell; his combative nature led to lengthy legal disputes over the amounts due and made him unpopular locally.

[1] The methods adopted by the Gell brothers included seizing property in lieu of unpaid Duchy rents or Ship money, causing widespread local resentment.

[6] As a Presbyterian, Gell's sympathies generally lay with Parliament, but the importance of the Derbyshire lead mines for manufacturing ammunition meant Charles unsuccessfully tried to win his support.

He followed up by plundering Elvaston Castle, former residence of Sir John Stanhope, allegedly defacing his tomb in the local church and digging up his flower beds.

Although an energetic and capable soldier, his bullying of the Derbyshire county committee and the plundering for which his unpaid troops became notorious provoked numerous complaints to Parliament.

He reportedly ignored orders from Sir Thomas Fairfax to bring his troops to Naseby in June, then was reprimanded for allowing 3,000 cavalry from the defeated Royalist army to escape him at Ashbourne.

[10] As the war came to an end in April 1646, it was discovered that he was negotiating more favourable terms with the Royalist garrison of Tutbury Castle than those offered by his colleague Sir William Brereton.

[12] During the Interregnum in 1650, he was involved in a conspiracy to restore Charles II led by the Royalist lawyer Eusebius Andrews, who was acting on his behalf in his divorce proceedings with Mary Stanhope.