Pensions UK estimates a comfortable retirement requires at least £45,400 a year, yet the full UK State Pension pays just £12,547.60 a year. Country State Pension Minimum (Euros) State Pension Minimum (Pound Sterling) Luxembourg €29,232.48 £25,004.54 Netherlands €19,650.84 £16,836.94 Austria €15,700.68 £13,452.42 Ireland €15,567.60 £13,338.40 Spain €12,441.84 £10,660.23 Belgium €11,688.48 £10,014.75 France €9,075.48 £7,775.92 Italy €7,437.48 £6,372.47The good news is there's a far better way for UK investors to secure their own retirement rather than relying solely on the government. Building a bigger pension potInvesting in the stock market through tax-efficient vehicles like a Self-Invested Personal Pension (SIPP) allows anyone to build their own retirement pot on top of whatever the State Pension eventually pays. But of course, the golden question is, which UK stock should investors be considering for their SIPPs? Well, according to institutional analysts, Rolls-Royce (LSE:RR.)