Paul - what you are proposing is a covered call, and is, IMHO, a safer strategy than holding the shares on their own.
As I write, HBOS is at 792. The October 850 calls can be sold for 21.5 (£215 per contract of 1000 shares). You keep the premium taken under all circumstances. If the shares are below 850 at expiry in October, then you keep the shares. If the shares rise to (say) 900 by expiry, then you will have the shares called away at 850, although you still keep the premium taken of 21.5, making the effective disposal price 871.5, so you have missed out on some of the gain.
If the price falls to (say) 750 and you decide to sell them, then you still keep the premium, making the effective disposal price 771.5.
If you can take a premium of 20 every 3 months, then you will take in 80 during the year, or about 10% of the value of the shares. So if the shares have a dividend yield of say 4% and rise in value by 5% over the 12 month period, then the overall return will be 10% + 4% + 5% = 19% of which over half comes from the option premiums taken in.
If you decide to sell the shares, then you should consider buying back the options as well. Once the shares are sold, the calls become uncovered and in the event of a runaway rally, or a take-over bid at (say) 1200, then you will have to deliver the shares at the strike price, 850 in this case, and the only place you will be able to get them is by buying them in the open market at 1200, and then delivering them for 850 - not a great money-making strategy!
Although I have not done it for some time (perhaps I should start again!), covered calls have been a great low risk strategy. I have also used the premiums taken in by selling calls to buy a put below the price before going on holiday so that I am protected against a major fall in my absence. If you match the prices, then the strategy costs you nothing. The best example was when I held Abbey National shares at 702 last Sept. I sold April 2003 750 calls for 53 and used the premium to buy April 600 puts for 44, leaving me with a credit of 9, and I was protected against falls below 600. When the price collapsed to 512 I was protected against falls below 600. I sold the shares at 623 for a loss of 81p per share. I bought back the calls for next to nothing, and held onto the puts which I held until April when I sold them for 212 which more than compensated for the 81p loss.
An excellent site on covered call strategies in the UK try :-
http://www.investorprofit.com