Unit trusts and gold certificates will be your safest option, but you investment will not be leveraged ("as sensitive" in your words) and will move in %ge terms along with gold. Commissions will be fairly noticable. However as long as the company is reputable and regulated you can 'buy and forget' for as long as you are happy that gold is on the up.
Gold shares are more risky option. I own a couple of New York SE-listed (eg Gold Fields, GFI) in my self-select ISA with i-dealing.com; which I can buy and sell at minimal cost There is a strong leverage effect with these un-hedged producers because a small change in the price of gold will have a disproportionatly large effect on profitability. Obviously this makes them a relatively high risk investment, which you shouldn't be betting your pension on, and individual firms will have their ups and downs that are unrelated to gold price.
For short term trading the vehicle of choice is perhaps the e-mini future YG which trades on the ECBOT. A $1 fall in the price of gold will decrease the value of the one contract by about $33.2. Commission costs on the buying and selling will be around $5 per contract, depending on broker. Some spread-betting firms will offer quotes based on this contract, at greater cost per round-trip but easier to set up an account.
Depends really on how much risk you are comfortable with and how actively you intend to manage your account. Futures and spreadbets will need to be attended to (rolled over etc) every few months as a minimum, for example, and require a high level of background knowledge. Few participants in these markets are consistantly profitable.
pete
