The average fund in the UK All Companies sector was up 5.1% between 12 December and 10 January, according to AJ Bell.

Smaller companies funds dominated the best performers list, with the top trust – JPMorgan Smaller Companies – up 15.74% during the period.

The top open-ended fund – VT Teviot UK Smaller Companies – was up 11.34%.

Laura Suter, personal finance analyst at AJ Bell, said: “The large majority gained by the Conservatives fuelled a Boris Bounce as investors hurried back into domestically focused companies that had been out of favour for so long.

“This can be seen clearly in the dominance of smaller company funds at the top of the performance tables.”

Investment trusts have done particularly well since Boris Johnson entered number 10, with the average trust in the UK All Companies sector up 8.2% and the average UK Smaller Companies trust up 8%.

“UK- focused investment trusts had been on stubbornly wide discounts to their net asset value in the lead-up to the election but benefited from a boost to share prices in the Boris rally as investors bid up UK stocks,” said Suter.

The managers of the top-performing JPMorgan Smaller Companies trust, Georgina Brittain and Katen Patel, seek to own companies with a competitive edge, frequently operating in niche growth markets, which rather than being dependent on GDP are forging their own growth.

Portfolio holdings include fantasy miniatures maker Games Workshop, specialist media group Future, and scientific instruments maker Judges Scientific.

The top fund, VT Teviot UK Smaller Companies, is managed by Scotland-based Valu-trac and focuses on the smallest 10% of companies in the UK market so it benefited from the boost to small UK firms.