OK, reading Dr John Whites investing in stocks and shares book and he mentions Yield Gap as part of the logical investment strategy, but does not define how to calculate. All I know is that it something to do with the yield difference between Shares and Bonds. Anyone help me with a definition on how to calculate it?

http://glossary.reuters.com/index.php/Yield_Gap

The basic idea is that if you invest in a share, it should pay you more than if you invested the same amount in a long-term government bond... which is widely considered to be the safest way to keep money. The difference between what you earn by holding a share and what you earn by holding the government bond (Treasury Bill) is your yield gap.

In practical terms, for the layman, you should only consider how much better an investment is than putting your money in NS&I bonds.

Brilliant but let me make sure I have understood this.

If I buy a share in company x @ y pence, then the rise/fall in price PLUS accrued dividend must be positive if the yield gap is to be deemed good then it must be greater than y pence invested in a bond at the same time.