HS2 is negotiating to buy more buildings, despite a government review due in October into whether the project should continue.
Costs have risen from £62bn to between £81bn and £88bn. The line is expected to open between 2028 and 2031.
HS2 said it "seeks a fair deal for both claimants and the taxpayer".
A spokesman said: "Every home, business and piece of land is unique and we appreciate that there may often be different opinions between owners, their professional advisers and HS2 about the value of a property.
"We work with the people affected to reach agreement, recognising the differences in opinion can take time to resolve."
The high-speed rail line is designed to boost the UK's economy by cutting journey times between London and the Midlands and the north of England.
The freedom of information request from the Local Democracy Reporting Service revealed the total spend on buying property in London to be at least £1,256,089,849 as of 30 June.
Many of the properties purchased to make way for the railway are in west London, including in Prime Minister Boris Johnson's constituency of Uxbridge and South Ruislip.
HS2 refused to release addresses, stating that this would risk exposing the empty properties to the risk of squatters.
Additional money has been spent acquiring 54 residential properties under private agreement and discretionary schemes, including commercial or industrial buildings in Uxbridge, Northolt, Camden and Westminster.
Amanda Souter lives beside Old Oak Common in East Acton, where construction has begun ahead of a planned HS2 station.
She said: "It should be cancelled, because there is no business case, it's costing too much, and it's out of control."
The Department for Transport has been approached for comment.
More than £1.25bn has been spent buying London properties to make way for High Speed Rail 2 (HS2), a freedom of information request has revealed.