The £1.5bn Marlborough Special Situations fund is the absolute best performing open-ended fund since Isa accounts were launched in 1999, according to data from FE Analytics.
The data covers the period from 6 April 1999 to 18 February 2018.
The fund is managed by Giles Hargreave and has been an average performer over the past year to 21 February, returning 18 per cent, compared with the 17 per cent return for the average fund in the IA UK Smaller Companies sector in the same time period.
But since 1999, the fund has returned 2,600 per cent.
The next best performing fund is Artemis UK Smaller Companies.
This is a £476m fund that has returned 1,505 per cent since 1999 and has been managed since 2007 by Mark Niznik.
Over the past decade the fund has returned 180 per cent compared with 139 per cent for the average fund in the IA UK Smaller Companies sector in the same time period.
The £770m Stewart Investors Asia Pacific fund was the next best performer, returning 1,410 per cent since launch in 2001.
The fund was managed for the first 15 years of its existence by Angus Tulloch, who retired in 2017, and is soft-closed to new investors.
|Marlborough Special Situations||2600|
|Artemis UK Smaller Companies||1505|
|Stewart Investors Asia Pacific||1410|
|Baring Hong Kong China TR||1279|
|Threadneedle European Smaller Companies||1263|
|BlackRock UK Smaller Companies||1220|
|Janus Henderson China Opportunities||1179|
|Baillie Gifford Emerging Markets Growth||1080|
|The MI Discretionary Unit||1069|
|Stewart Investors Global Emerging Markets||1024|
|Aberdeen Emerging Markets Equity||992|
|Janus Henderson European Smaller Companies||975|
|Standard Life Investments UK Smaller Companies||970|
|TB Amati UK Smaller Companies||954|
|Baring Europe Select||953|
|Liontrust UK Smaller Companies||912|
|Invesco Perpetual Hong Kong & China||883|
|Invesco Perpetual Asian||845|
|Invesco Perpetual UK Smaller Companies Equity||825|
In the world of investment trusts, the top two in performance terms since 1999 are the Scottish Oriental Smaller Companies trust, which is run by First State, and the Aberdeen Asian Smaller Companies Trust.
The First State Trust has returned 2,943 per cent from 1 April 1999 to 31 January 2018, according to data from Morningstar.
Mr Tulloch was also the founder of this trust.
The Aberdeen Asian Smaller Companies trust has returned 2,604 per cent in that time.
The Janus Henderson UK Strategic Income is the only surviving fund to have lost investors' money over this time frame, delivering minus 14.16 per cent compared to the IA equity income sector returning 204 per cent.
Adrian Lowcock, investment director at Architas said: "Markets have been anything other than normal in the years since Isas were launched, which is pretty much in keeping with any other period in history.
"The backdrop to investing is always changing and makes it hard to predict where the stock market returns might be over the next 20 years."
The data shows the importance of being diversified as well as having the right funds in your portfolio, Mr Lowcock said.
While passive investing has been a good strategy following the financial crisis, Mr Lowcock said the data showed there are still areas which benefit from active management, including smaller companies, Asia and emerging markets.