Shares in Impax Asset Management (IPX) shares tumbled 12% this morning as the fund manager revealed a sharp slowdown in its six-month inflows, with the fall leaving the stock trading at less than half of its value at the beginning of the year.

The sustainable champion enjoyed an extraordinary rerating over the two years to 2022, but has now seen that momentum dramatically reverse as its core growth stocks have fallen from favour.

While the company reported £2.5bn in inflows over the half year to the end of March, that was a run rate of about 50% of the sales achieved in the full year to the end of September.

The cooling in sentiment has seen Impax Environmental Markets (IEM ), its £1.3bn investment trust, de-rate. Shares that stood at a 15% premium over net asset value last November, worrying its board that it might not be able to keep up with investor demand, have slipped to a 3% discount to NAV. This follows a 22% fall in the shares this year, though longer-term returns have so far held up with shareholders enjoying a 90% total return over five years.

Impax ‘pleased’

The run-up to the end of the tax year in April is historically responsible for a disproportionate share of full-year fund flows, as investors rush to take advantage of their ISA and Sipp allowances.

Assets stood at £38bn at period end, 8.1% lower over the three months. Since the period end, assets have slid further to £37bn.

Adjusted operating profit for the period was £34m, up from £20m in the same period of 2021 but marginally lower than the £35.1m reported at the end of last year.

Revenue of £88.6m was well above the £60m of a year earlier and the £82.5m of late last year, offset by the cost of a hiring spree which lifted outgoings to £54.7m, from £38.9m a year before.

Chief executive Ian Simms said: ‘Impax has delivered a solid first half to its financial year.

‘Our investment approach, with its careful attention to risk and resilience, continues to attract asset owners that are seeking to build robust portfolios with attractive returns, focused on the transition to a more sustainable economy.

‘Amid considerable market volatility surrounding recent geopolitical events, we continue to be pleased with the long-term performance of our investment strategies.’

The house lifted its interim dividend from 3.6p to 4.7p. Despite the fall this year the stock remains more than 630% up over the last five years.