Chancellor Philip Hammond will seek to reassure businesses they will still be able to get access to investment funding as Britain withdraws from the European Union.
In his annual Mansion House address to City leaders, Mr Hammond will say ministers are in discussion with the European Investment Bank (EIB) to ensure UK projects can access its funds during the remaining period of Britain's EU membership.
Current EIB lending to the UK is worth around 48 billion euros (£42 billion) and has supported projects such as new Intercity and London Underground trains and new tram networks in Manchester and Nottingham.
At the same time he will say that the UK's own financing schemes stand ready to provide additional support and certainty to investors.
The British Business Bank (BBB) will extend the limits of its venture capital investment programme to enable it to provide greater levels of investment into individual funds that would otherwise struggle to raise capital.
If necessary, Mr Hammond will say, he is ready to bring forward some of the £400 million in additional investment which he announced in last year's Autumn Statement.
The Treasury estimates that in the short-term, up to £80 million could be released, unlocking up to £320 million of total investment in the coming months.
Meanwhile, the UK Guarantee Scheme will offer new types of financial support to help complex projects to reduce the risk they face and to access private finance.
Mr Hammond will say: "Investors need certainty in order to continue to support the UK economy and create jobs as we leave the EU.
"That is why we will fortify the vital financial support that helps businesses to grow - from cutting edge start-ups right through to large scale infrastructure projects."