The prime minister visited a construction site on the South Bank early on Tuesday morning.
David Cameron visited the building site at 199 Westminster Bridge Road where a new 1,000-bedroom student residence and private sixth form college is under construction.
"Giving businesses the confidence to invest and create jobs is a key part of our long term economic plan," said David Cameron.
"Balfour Beatty's commitment to spend a record £1 billion on small and medium sized businesses this year is very welcome evidence that this plan is working – supporting thousands of jobs within small and medium businesses, which will give hard-working people economic security for the future."
Nicholas Pollard, Chief Executive Officer, Balfour Beatty Construction Services UK, said: "We are delighted the Prime Minister could be with us today to celebrate our £1 billion spend with small businesses this year, 98% of which are British companies. Small businesses create local jobs and apprenticeships and they are the innovators, engineers and exporters of the future. We are committed to supporting them so that we can build a better Britain together; leaving a lasting legacy in the communities we touch across the UK."
Jonathan Howard, director of SE1-based firm Robert West, a small business providing temporary works and scaffolding which is working on the student accommodation project, said: "We have seen that Balfour Beatty is committed to close and collaborative relationships with locally-based small businesses like ourselves.
"The stability of our relationship with Balfour Beatty allows us to thrive and progress as a business and we welcome additional investment being targeted at smaller businesses like ours.
"We certainly support Balfour Beatty's commitment to increasing spending with small and growing businesses like ours."
The scheme being developed by Urbanest includes new premises for DLD College London.