LONDON -- The last five years have been tough for those in retirement. Portfolio valuations have been hammered, and annuity rates have plunged. There's no sign of things improving anytime soon, either, as the eurozone and the U.K. economy look set to muddle through at best for some years to come.

A great way to protect yourself from the downturn, however, is to build your retirement fund with shares of large, well-run companies that should grow their earnings steadily over the coming decades. Over time, such investments ought to result in rising dividends and inflation-beating capital growth.

In this series, I'm tracking down the U.K. large-caps that have the potential to beat the FTSE 100 (UKX) over the long term and support a lower-risk income-generating retirement fund (you can see all of the companies I've covered so far on this page).

Over the last few weeks, I've looked at 15 shares, and in this article, I'm going to examine the five lowest-scoring shares -- Royal Bank of Scotland Group (LSE:RBS), Lloyds Banking Group (LSE:LLOY), Smiths Group (LSE:SMIN), Shire (LSE:SHP) and Admiral (LSE:ADM).

First, let's take a look at how each of them scored against my five key retirement share criteria:

CriteriaRBSLloydsShireAdmiralSmiths Group
Longevity 5/5 5/5 2/5 2/5 5/5
Performance vs. FTSE 1/5 2/5 4/5 3/5 3/5
Financial strength 3/5 3/5 4/5 4/5 3/5
EPS growth 1/5 2/5 4/5 4/5 4/5
Dividend growth 1/5 1/5 2/5 4/5 2/5
Total 11/25 13/25 16/25 17/25 17/25

RBS & Lloyds
The U.K.'s disgraced duo of bailed-out banks continues to feature regularly in the headlines and attract negative publicity. Yet investors clearly think that much of the noise is irrelevant and that the banks' recovery prospects are good -- Lloyds' share price has risen by 79% so far this year, while RBS shareholders have enjoyed a 48% gain. Despite these strong gains, shares in both banks remain around 90% below peak levels, and shareholders who bought during the boom may never get their money back.

So could either of these banks turn out to be a good retirement share for new investors? Although both banks' shares trade at a discount to their net asset value, neither bank currently pays a dividend to ordinary shareholders, and big question marks remain over the quality of their loan books. Bank of England Governor Mervyn King recently suggested that U.K. banks are showing unusual forbearance to borrowers who are in arrears, so that the banks can avoid being forced to write-off any more bad debt.

While both banks offer potential value, I think they are too risky as retirement shares, even if you aren't planning to retire for many more years.

Shire
High-flying pharmaceutical firm Shire built its reputation (and profits) on its market-leading attention deficit and hyperactivity disorder (ADHD) drugs. In FTSE 100 terms, it's something of a youngster, having only been in existence for 26 years, and this hints at its weakness as a retirement share -- it's still a highly rated growth share with a price to earnings ratio (P/E) of almost 20 and a dividend yield of just 0.5%.

It's entirely possible that Shire's success will continue and that one day it will offer an attractive yield at a sensible price -- but this kind of growth investing is not compatible with my requirements for a retirement share, which are built around sustainable earnings growth and an attractive dividend yield. Retirement investors looking for a pharmaceutical share would be far better served by either GlaxoSmithKline or Astra Zeneca.

Admiral
Car insurance group Admiral is a well-known brand in the U.K., where it also operates the Confused.com price comparison website. Further afield, Admiral is working hard to expand its presence in the large U.S. market, but the U.K. is still its bread and butter -- and its primary source of profit. A recent arrival in the FTSE 100, with less than 20 years to its name, Admiral's profitability has been highly impressive, and investors have liked its generous dividends and strong growth.

However, there were signs that it was too good to last -- and the company's most recent trading update confirmed this, revealing a 5% fall in U.K. car insurance turnover during the third quarter. My conclusion was that Admiral's business is sound enough, but that more attractive insurance shares exist for retirement investors. I prefer Aviva or RSA Insurance, both of which have a more diverse business mix, longer histories, and far more attractive dividend yields.

Smiths Group
Smiths Group offers investors access to a wide range of technology and engineering businesses, straddling the medical, energy, security and aviation sectors. Its 3.6% dividend yield is slightly above the FTSE 100 average and it enjoys quite high profit margins. Financially it seems sound -- although its debt load is quite high -- so if you are looking for an engineering-focused retirement share, it might be worth a look.

Before your finger starts twitching over the buy button, however, you might want to consider Smiths' relatively poor dividend growth. The average dividend growth rate over the last five years has been just 2.8% per year -- below most realistic measures of inflation. Unless the company manages to reduce its debt load and improve its payout ratio, you could be stuck with a fairly average income for many more years, with little prospect of the yield on cost gains that make the best retirement shares so attractive.

Learn from the best
Doing your own research is important, but another good way of identifying great dividend-paying shares is to study the choices of successful professional investors. One of the most successful income investors currently working in the City is fund manager Neil Woodford, who had 21 billion pounds of private investors' funds under management at the end of October 2012 -- more than any other City manager.

Woodford's track record is truly outstanding. His High Income fund grew by a staggering 342% in the 15 years to 31 October 2012, during which time the FTSE All-Share index only managed a gain of 125%.

You can learn about all eight of Neil Woodford's top holdings and see how he generates such fantastic profits in this free Motley Fool report. Many of Woodford's choices look like excellent retirement shares to me, and the report explains how he chose some of his biggest holdings.

This report is completely free, and I strongly recommend you click here to download this report today, as it will be available for a limited time only.

Roland owns shares in Aviva and GlaxoSmithKline but does not own shares in any of the other companies mentioned in this article. The Motley Fool has a disclosure policy. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. Try any of our Foolish newsletter services free for 30 days.