Looking on the internet deeply has found these results:

I have been in London at least 7 years is the most popular phrase on the web.

I have been in London for 7 years 16 results on the web	I have been in London at least 7 years 1541,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
We'd been in London for three months trying to nail down British Petroleum. She and her husband have been in London for two years. My parents have been in London. The boy's mother has been in London for a year already. My parents have been in London. Following the attacks in London on 7 July this year, the Council held an extraordinary meeting on 13 July. Detective, I have checked, and Hanna's father has been in London for the past three months. No, Papa can't have been in London.	I have to be in training until at least 7:00. I haven't been in London since... She and her husband have been in London for two years. Following the attacks in London on 7 July this year, the Council held an extraordinary meeting on 13 July. There was a neighbour when we used to live in another street, not here... a man, younger than me, Younger by at least 7 years. My parents have been in London. My parents have been in London. No, Papa can't have been in London.

I have been in London for 7 years

16 results on the web

I have been in London at least 7 years

1541,000,000 results on the web

More popular!

We'd been in London for three months trying to nail down British Petroleum.
She and her husband have been in London for two years.
My parents have been in London.
The boy's mother has been in London for a year already.
My parents have been in London.
Following the attacks in London on 7 July this year, the Council held an extraordinary meeting on 13 July.
Detective, I have checked, and Hanna's father has been in London for the past three months.
No, Papa can't have been in London.

I have to be in training until at least 7:00.
I haven't been in London since...
She and her husband have been in London for two years.
Following the attacks in London on 7 July this year, the Council held an extraordinary meeting on 13 July.
There was a neighbour when we used to live in another street, not here... a man, younger than me, Younger by at least 7 years.
My parents have been in London.
My parents have been in London.
No, Papa can't have been in London.