Sorry for the delay to this. Anyway, in the aftermath of Cade's rebellion and the English expulsion from Normandy, England was a very discontented place. There were lots of discharged soldiers wandering around London, and the arrival of York in October (from Ireland) added to the tense atmosphere as preparations began for Parliament to meet. Various seditious 'bills' were nailed to the doors of St Paul's, Westminster Hall, and even the King's chamber at Westminster!
On 1 December there was an actual rising against Somerset, an attack by more than 1000 men. He was (for his own protection) taken by barge to the Tower, while order was maintained by York, Devon and the Mayor, apparently the only people for whom the insurgents had any respect.
The Parliament petitioned for the removal of Somerset (and others, including the Dowager Duchess of Suffolk) from the King's presence, but Henry managed to evade this demand, and when Parliament was prorogued in May 1451 the pressure on Henry's favourites eased for a time. Somerset was actually appointed Captain of Calais, presumably on the basis that he wouldn't dare to lose that as well. (On the face of it, you'd have thought him the last person eligible for the job.)
In 1452, despairing of removing Somerset by peaceful means, York rose in arms. However he was joined only by Devon and Cobham, and was forced to submit to the King at Dartford. Though swiftly pardoned, in return for swearing never to rebel again, the affair had brought about his total humiliation and strengthened Somerset's position immeasurably.
Unfortunately for Somerset, about the beginning of August 1453, Henry VI had a complete mental collapse. This coincided roughly with the news that Talbot (Shrewsbury) had been defeated and killed at Castillon in Gascony, with the result that English rule in France (barring Calais) was over. In addition, Queen Margaret of Anjou had lately announced that she was pregnant. While either of these events might have added to Henry's stress and pushed him over the edge, it's dangerous to assume that they did.
At first the King's illness was kept quiet, but in October 1453 a Great Council was held - equivalent to a sort of slimmed-down Parliament. Somerset tried to exclude York, but this led to representations, including one from Duchess Cicely to the Queen, and York was sent a belated invitation.
York's supporters now included the Nevilles (alienated by Somerset over the small matter of Glamorgan) and the Duke of Norfolk. It was actually Norfolk who appealed Somerset of treason, mainly based on his failure in France. As a result Somerset was taken to the Tower where he remained for about a year. No charges were brought.
York was not actually named Protector until late March 1454, an alternative proposal that Queen Margaret act as Regent having been dismissed on grounds of precedent.
King Henry recovered (or was said to have done so) around Christmas 1454, and on 26 January 1455 Somerset was released from the Tower, though the release was not actually confirmed until a meeting of the Great Council on 5 February. Soon afterwards York resigned as Protector and, in effect, Somerset regained power. All charges against Somerset were dropped and arrangements were made for a panel of arbitrators to settle all disputes between him and York.
York and the Nevilles now decided that the time for talking and playing politics was over. They believed that Somerset and his clique were poisoning the King's mind against them and that in fact they were not safe to approach Henry in the normal way. Under this belief or pretext they marched to St Alban's at the head of about 7000 men and there met Henry and his court on their way to a further Great Council meeting that had been arranged for Leicester.
York demanded that Somerset should be handed over to him, and when this was refused, the Yorkists attacked. Somerset, having killed four men with his own hand, was slain in the fighting, along with the Earl of Northumberland and Lord Clifford. Their deaths brought the battle to an end, but not unnaturally filled their sons with a burning passion for revenge.