"There is an argument to say, well, you know, let's invest in those companies to help them transition. The way we would look at that from an impact investing point of view is, at the end of the day, the end product is still oil. So it really depends upon the company itself."
If they are the "right" businesses, he recognised the importance of helping them transition over, he said.
Regulating the 'wild west of greenwash'
To get to the level of detail he needs to get to in order to select the right investment targets, Armstrong uses a number of discretionary fund manager partners for research purposes, as well as doing his own research.
This was "to really whittle down and make sure that when we lift the hood and really look at the detail, actually what we're presenting to clients is what we say we're doing," he said.
He added the level of company reporting was still a challenge with "an awful long way to go" but it has been getting better.
Armstrong believes ESG and its definition should be regulated.
The Financial Conduct Authority is currently drawing up rules for investment labels, which should allow investors to make more informed decisions on ESG strategies.
"It's the first stepping stone," said Armstrong. "It's good that we're getting some regulation in to try and stop the wild west of greenwash, whether it's going to meet what we need as an industry to get to where we need to get to in terms of complete clarity I don't know yet."
The FCA is also mulling rules for advisers, effectively forcing them to raise ESG with their clients. But Armstrong warned this could end up becoming a 'tick-box exercise" for advisers.
"We need to make sure as advisers we're having the right conversations with clients about really exploring their values," he said.
"It's our job to make sure that we're bringing sustainable and impact investing to our clients to explain to them what it is and not wait for them to ask."
He said the main point was to give clients a choice of options, not to "layer on our own beliefs".
When it comes to investing, choice has proliferated as the market matured, which has made it easier to build portfolios, Armstrong says.
"Initially, we might have had to have a heavier weighting in cash because there might not have been as good bond structures as there are now but there's more and more bonds coming online as the market matures so it's getting easier and easier," he said.
Blue Sphere has deliberately positioned itself as an impact investing-focused advice firm. The reason, said Armstrong, was ideological.
"We've nailed our colours to impact investing because as a business we want, and I particularly want for my family, to have at least done the best that I can do in terms of what we can for climate change and for the environment and for people.