A German landlord has emerged as one of the biggest investors in London property in recent years.

Henning Conle, 70, has snapped up almost £2bn of prime real estate, including a series of historic buildings in central London, raising inevitable questions about where he got his money from.

The portfolio includes buildings that house department stores such as Liberty and House of Fraser, the Kensington Roof Gardens complex, the London offices of Manchester United and the art deco Shell Mex House on the Strand.

Until now, little has been known about Conle and the Liechtenstein-registered Sirosa company he uses. When the Shell Mex deal was concluded for a reported £610m last year, press reports identified the buyer as a German family named “Conley”, a typing error that inadvertently helped to disguise the owner.

Kensington Roof Gardens. Photograph: Jonathan Perugia/Rex Features

Conle has a somewhat tarnished reputation in his native land, where he is thought to own more than 10,000 properties.

In Hamburg, in the 1990s he owned up to 2,500 flats.

Tenants complained about bullying tactics. In 1998, a Hamburg court ruled that Conle had used illegal methods against tenants who were late with their payments, leaving threatening notices up in public hallways.

There has been speculation that Conle may be investing money from other clients, possibly even from Russia – but the landlord denies this. In a statement, he said: “The properties [in London] were financed by means of bank credits and capital resources. It is untrue that the purchases were carried out as a facade for investors from eastern Europe.”

Shell Mex House. Photograph: John Maclean/View Pictures/Rex Features

In London, his growing empire is attracting notice in the property industry. “The name Sirosa was one of the names most spoken about in the central London real estate market last year, yet one of the most below-the-radar firms,” said Joanna Bourke, West End editor of Estates Gazette.

In the Ruhr region, where he grew up, Conle still owns many properties.

A Berlin property owned by Conle. Photograph: Philip Oltermann

The properties Conle has bought in London are all period buildings, four of them listed. The Grade II*-listed Liberty department store on Regent Street, which Conle acquired for £41.5m in 2010 , is one of the best-known mock-Tudor buildings in Britain.

Others, such as Barkers department store on Kensington High Street, Plaza shopping centre on Oxford Street and House of Fraser’s flagship store on the same street, are classic pieces of art nouveau architecture.

Over the last two years, Conle has also acquired the Grade II-listed Stratton House for £166m in 2012, which houses the London offices of Manchester United.

Last year, Sirosa outbid the Qatar Investment Authority to buy Kensington Roof Gardens, home to a Virgin luxury club and restaurant, for £25m over its £200m asking price, followed shortly afterwards by a swoop for Shell Mex House, for which Conle paid £116m more than the previous owner paid in 2007.

Financially, Conle’s investments have certainly made sense: the value of central London property grew steadily throughout the global financial crisis. One London estate agent who worked with Conle described investing in commercial property in the British capital as “a one-way bet. Residential can be incredibly messy, but commercial is a good place to park your money – it allows you to remain passive.”

Henning Conle comes from a family with a long – and often controversial – track record in property management. Father Heinz and uncle Kurt Conle, both from Mülheim, ran one of the leading architecture agencies in postwar Germany.

Over the course of the 1950s, the Conle brothers made a fortune on the back of the “economic miracle”, building up to 18,000 apartments and municipal buildings , allegedly using criminal methods to win contracts . In 1961, Heinz Conle was put on trial for having bribed a local official and embezzling public funds – the trial was discontinued in 1967, due to the death of brother Kurt.

• This article was amended on Monday 12 May 2014 to correct the spelling of Mülheim, and on Thursday 15 May 2014 to correct the country where Sirosa is registered from Luxembourg to Liechtenstein. Further amendments were made on Thursday 15 September 2016 and Monday 3 October 2016 following a German court ruling that certain claims made about Mr Conle were unfounded.