I am going to describe how immigrant Indians and upper-class British are the most distinctly opposite in terms of etiquette. The reason I have subdivided this into immigrant Indians and upper-class Brits as opposed to all Indians and all British is because there are so many other subgroups within each nationality that the amount of factors/feedback loops that can be contributing to differences in etiquette make it near-impossible to understand. My primary argument is that economic conditions influence culture, which in turn influences etiquette.
The stereotype is that British people are very calm, helpful, and inclusive. This is true mainly of the rich, upper-class. They share with other people, are very polite, and make an effort to ensure everyone is included. Historically, this was a class-based phenomenon. The upper class wanted to separate themselves from the common folk and etiquette part of this distinction. When walking around, this remains evident. Doors are held for others, seats are offered for others, and conversation among strangers is polite and easy.
On my way to England, our plane was delayed. We were sitting in the plane in the May in Florida with no A/C for 3 hours. It was hot. The plane never took off and was cancelled. From their accents, I found most all the passengers to be British born and raised. Many sported Disney merchandise and designer bags. I am going to make the totally anecdotal claim that they were primarily upper-class British folks traveling for vacation or leisure. Whilst sitting in the plane, the attitude among passengers was calm. I heard statements such as "it's not the pilot's fault, he can't do anything" and "it's okay we will just leave tomorrow". The general sentiment was pleasant even when we disembarked. Everyone formed an orderly line in front of the counter as the airline representatives answered questions people had.
Immigrant Indians are the opposite. If there is an opportunity available they do their very best to snatch it before someone else does. This mentality leads to fierce competition and a cutthroat attitude to life. Even parenting is a strong-willed endeavor. Immigrant Indian parents have high expectations for their children with a heavy emphasis on education. These childhoods are full of math, piano, and SAT prep. In short, an Indian American childhood is a disciplined childhood. It is no surprise that Indians are the richest ethnicity in the United States. But, do not expect doors to be held for you, a calm atmosphere in a delayed plane, or a seat given up for you.
The interesting thing is that these forms of etiquette actually shaped each other. The British maintained a strong hold on India for many years sucking resources and manpower out of the country. The British benefitted heavily from trade and exotic goods from India. Meanwhile, India was sunk into poverty and constraint. This led to a culture of splendor in upper class Britain and a culture of scarcity in much of India.
In the culture of the upper class British, sharing was permissible because there are more than enough resources for everyone. Well-fed, well-clothed people tend to be nicer and more polite. Their manners also allowed the to seperate themselves from the lower class. India has been a poor country with bleak economic prospects. In order to make it out of poverty, you must leave the country to a place with more opportunity. You must have a marketable, in-demand skill for another country to allow you entrance. This not only requires being smart, but being smarter than everyone else as many countries have quotas for the number of immigrants they accept from a given country. This scarcity-based mindset pervades everything that Indian people do, including their etiquette.
I want to talk about how etiquette has affected my life growing up. Raised in a half-indian, half-british-descented-american household, I have seen these cultural differences in real-life. I am more biased towards acting in the Indian manner, but there is a time and place for both. At the gym, I am Indian. If a machine is open I gun for it. There is fierce competition for machines in my university's busy gym and allowing others to go first means I will never get my workout in. It has gotten me into airport lounges for which I did not have the required credit card, entrance into buildings for which I did not have access, dates with people out of my league, and so much more. The upper class British mentality is necessary in situations that require a polite and calm demeanor. These would be situations like talking to wait staff at a restaurant, making small talk with strangers, or giving up a seat in the subway for an elderly lady.
I always find it funny watching these cultural differences clash. For the sake of comparison, I will substitute American upper-class for British upper-class as much of my experience with culture clash come from America. My rich American friends and family often find the scrappy immigrant attitude to be abrasive, rude, and overbearing. The immigrants find the Americans to be lazy, not in control of their own life, and unable to stick up for themselves. My take? They are both right!