UK share markets have had another false start at the start of 2021. After a blistering beginning to January the new bull market ran out of steam almost as quickly as it began. The long-running Covid-19 saga rolls on and continues to play havoc with investor confidence. And it threatens to derail a solid rebound in the global economy this year.

The muddy economic outlook isn’t stopping me from continuing to build my Stocks and Shares ISA, though. This is because there are still plenty of UK shares that I think could record big profits growth in 2021 regardless of the wider economic landscape. It’s also due to the fact that I invest with a view to making returns over a long-term time horizon.

2 UK shares on my ISA radar

It’s a bonus if they can provide faster returns, of course. Here are a couple of shares I’d happily buy for my own Stocks and Shares ISA that I think could start to do well in 2021.

#1: Tharisa

I have just explained why respondents to a London Bullion Market Association (LBMA) survey reckon silver prices will fly in 2021. The same investor concerns and macroeconomic factors (like low interest rates and a weak US dollar) that are anticipated to push the grey metal higher this year are expected to drive the prices of the platinum group metals (PGM) suite too.

The LBMA reckons that average platinum and palladium prices will rise 28.2% and 11.2% respectively in 2021. This creates averages of $1,131.50 and $2,439.10 for the two chief PGMs. The precious commodities are expected to benefit from improved car making as the economic recovery kicks in. And this bodes well for UK shares like Tharisa (LSE: THS), which haul the metals out of the earth.

There are significant risks to Tharisa, of course. The threat of production problems and spiralling costs are two ever-present problems for UK mining shares. Indeed, rampant Covid-19 infection rates and safety issues forced the company to shutter its operations at times in 2020. Still, in my opinion, the company’s low valuation makes it an attractive buy today. Tharisa trades on a price-to-earnings (P/E) ratio of 10 times for the fiscal year to September 2021.

#2: 4Imprint Group

I believe that marketing products maker 4Imprint Group is another good UK value share for 2021. This business trades on a forward price-to-earnings growth (PEG) ratio of 0.2. Any reading below 1 suggests that a stock is being undervalued by market makers.

I can understand why investors might be reluctant to pile into 4Imprint today. The prospect of a bumpy economic recovery could spell havoc for product orders at the company. But for the moment, trading continues to recover and January’s update showed its order intake improved to 70% of 2019 levels in the fourth quarter. This compares with a weekly average of 60% it recorded at the end of October. Advertising budgets recover quickly when economic conditions improve. And this could result in a blockbuster year at this UK share.