That's an insane hyperbole.
Gordon Brown (in the treasury) produced a report to see how UK could integrate with the EU. The output was basically that the UK economy is not flexible enough.
A very large portion of the UK's GDP is based on housing and housing services. The amount of debt on UK housing is astronomical.
http://news.bbc.co.uk/2/shared/spl/hi/europe/03/euro/pdf/fin... Page 55 onwards
"mortgage debt 60% of gdp"
http://www.ft.com/fastft/309012/how-would-uk-housing-correct...
http://www.thisismoney.co.uk/money/mortgageshome/article-234...
A slightly counter view with different numbers: http://pdf.euro.savills.co.uk/residential---other/spotlight-... : still points out that large amounts of UK assets are held overseas and that in 2013 there was $10bn of office property inward investment.
Also, I don't think that yield from real estate is classified under the "trade" item in the Balance of Payments