Some comments:
* £24 per quarter is competitive (ii charge £9.99 per month and also give rebates if you trade)
* buying £90 of equity at a time is much too small
* if you can find an ETF or IT with similar ideas to your own you can make one annual investment rather than twelve small ones
* consider some sort of equity based regular savings plan (not sure if IG offer this)
* you may be able to get better value for yourself by using spread betting or CFD (though they come with problems of their own). Try out a Demo account and if you then use a Live account, start with markets offering a Guaranteed Stop.