He said: "By growing internationally, it will make us more resilient and it will attract global clients and investors. We see it as the way forward. We now do BMW's environmental management work and we want more of those types of contract."
He made the comments as WSP posted a pre-tax profit of £5.4m for the six months to 30 June, up 37% on the same period last year. Turnover more than doubled to £96.2m.
More than 50% of WSP's business is outside the UK after acquisitions in the USA and Sweden, but Cole said he was prepared to make further purchases.
Earlier this year, WSP bought Swedish consultancy Jacobson and Widmark for £72.5m, making it the third largest consultant in Europe.
Cole said the test for the enlarged group would be if it won contracts either company on its own would not have.
He said: "We're as big as anyone in the UK. We are already in the USA, Asia, Scandinavia and Africa. Through J&W we want to move into eastern Europe. We see real opportunities there for us and we're just scratching the surface at the moment."
WSP's biggest clients in the UK include BAA, the Highways Agency, Canary Wharf and GlaxoSmithKline.
