I work in insurance and I don't think that having an excess of say £150 is going to make much difference. Most people don't bother claiming for small losses so I would imagine that if you claim it is going to be for something quite costly. For instance if you make a claim for £1000, whether you have no excess or an excess of £150 isn't going to make much difference as far as the insurance company are concerned. They will still have paid out far more than you have paid them in premiums for the year. I wouldn't bother with a voluntary excess unless your primary concern is to keep your premium down. You might find that you do still have a compulsory excess anyway, and the voluntary excess is in addition to that.