The gilts in question are the TN25 and TN24, ii found, which made it to the index due to the recent surge in bond yields and the subsequent rise in popularity of bonds, as interest rates are expected to remain higher for longer.
The investment platform said portfolio weightings to bonds have also seen an uptick, with allocations to fixed income and corporate bonds increasing from 0.6% in Q1 2021 to 0.8% in Q4 2022 and 2% in Q3 2023.
Sam Benstead, bonds specialist at interactive investor, said investors were taking advantage of high interest rates by moving their money into the bond market, where he said they are "finally being rewarded with attractive yields", with gilts now paying between 4.5% and 5% a year carrying an "effectively zero" risk of default.
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"Gilts come with the added bonus of being capital gains tax free, which has boosted the appeal of low coupon bonds set to mature soon, where the vast majority on the total return comes from capital appreciation when the bonds mature," he explained.
Benstead noted that bonds higher up the risk spectrum, including investment grade and high yield corporate bonds, yield even more. However, he warned that bonds were not risk free.
"While the income from gilts and the return of their principal is secure, their prices can still be volatile, particularly those with a long time before maturity," he said.
"Investors reprice bonds based on their expectations for interest rates and inflation, so an unexpected rise in interest rate expectations can spook the bond market, sending prices down and yields higher."
When value was taken into consideration, the top ten holdings among all age cohorts were dominated by passive strategies, all from Vanguard. Those aged over 65, however, opted for a combination of active funds, investment trusts and FTSE 100 dividend payers.
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Investment trusts continued to prove popular among retail investors, with the Alliance Trust dominating the top spot across all age bands.
When ii's index was first published four years ago, Scottish Mortgage investment trust was the most held stock across those aged 24+. After suffering significant share price falls, the trust has lost its top spot, though it remained in the top ten across age categories.
Despite the domination of passives, ii found active managers have not fallen out of favour with investors. Fundsmith Equity was the most held fund by investors overall, while the Vanguard Life Strategy 80% Equity, which invests in passive instruments, was the most held fund in the 35 to 44-year-old bracket.
The platform also noted its youngest and oldest customers have avoided the big US tech brands, while companies such as Apple and Tesla were among the most held for the middle cohorts.
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Richard Wilson, CEO of interactive investor, said: "Our private investor performance index continues to be the only barometer of its kind to truly take the temperature of how retail investors are faring in these extraordinary times.
"In an ever-changing world, customers are sticking with solid long-term strategies, avoiding knee-jerk reactions, and patently building long term wealth. But they are also open to potential new opportunities, with bonds looking more interesting as yields have risen. We continue to publish content to help customers navigate this asset class and assess the risks.
"Customers continue to embrace active and passive strategies using a combination of funds, investment trusts and ETFs, while also looking to UK and US shares."