How did the wily British put the noose around prosperous Bengal?

Aliwardi Khan,Nawob of Bengal),India. www.
After the death of the Mogul Emperor Aurangazeb (on 20th February,1707), who openly discriminated against the Hindus and engaged in several wars against other kingdoms, especially Marathas (which drove the Mogul Empire to the brink of bankruptcy), an ideal situation developed for the  British to take control over Bengal using various excuses. In fact, the British traders had been patiently waiting for this wonderful opportunity for decades. They never thought that such a situation would brew to the brim so soon. While rest of India was replete with turmoil- fratricidal wars, Maratha invasion, Jat uprising, etc Bengal was quiet and well administrated. The recent devastation caused by the unexpected invasion and plundering of Nadir Shaw from Persia left the Mogul ruler bewildered and exasperated. It took a beating on Mogul's power and prosperity. Cracks developed in their powerful hold on the Indian subcontinent. While elsewhere particularly  in many north Indian kingdom a chaotic situation was prevailing, Bengal under Alivardi Khan, had been prosperous, peaceful and paradise; well progressed in agriculture, industry and banking as was illustrated by Jagat Seth,banker's banker;  a haven for wheeling and dealing.

After his death in 1756 Siraj-ud-daulah, his grandson (daughter's son) became the ruler. He was young and incompetent. Since the time of Aliwardi Khan, the British had been purposely violating their trade privileges granted to them by Farrukhsiyar in 1717 – building further fortification, strengthening their garrison at Fort. William, Calcutta without written permission from the young Nawob. The company made huge profit by fraudulent use of Dastak (free trade pass). They carried on Customs free trade. Export-import taxes remained unpaid for a pretty long time. A great financial loss for the Bengal ruler.

Their over interference in the Nawob's administration and insulting responses angered the Nawob. Provocations and counter provocations led to animosity and hatred between the ruler and the British. On June 4th 1756 the Nawob's army captured the company's factory at Kasim Bazaar and on 20th captured Calcutta. This resulted in  'Black Hole (of Calcutta) tragedy and the casualties became controversial. This incident became a trump card for the British to  justify their stay in India and their military actions against the Indian rulers. This paved the way for the entry of Robert Clive into Bengal from Madras who was fresh from victory over the French led by Dupleix along with Chanda Shaib. 

In 1733 the Nawob of Bengal  complained  about the English traders and their untrustworthy British company. It was something like this ....

When they first came into the country they petitioned the then government in humble manner for liberty to purchase a spot of ground to build a factory house upon, which  no sooner granted, they built a strong
Map of early Bengal credit www.
fort, dug  a ditch  around it to have  communication with the nearby river and mounted a great number of guns upon the walls. They  enticed several merchants and others to go along with them and take protection under them and  collected a revenue which ran into
o Rs 10,00,000.00 ... they robbed,plundered and carried great number of the king’s subjects of both sexes into slavery in their own country …...

At last they reached the final stage of putting the noose around the Nawob and his country after the battles at Plassey (June, 1757) and Buxar (october,1764).