Weight loss - no problem; Fat loss - not quite so easy!

I hope someone may be able to help.

I would say I am a natural ectomorph in terms of physique. Small boned wiry frame, find it difficult to put much weight on no matter what I eat. This is lucky in many respects as I do not have a natural propensity to get fat, and a little discipline makes it easy for me to lose weight overall.

However, I am currently working very hard to reduce my body fat percentage (BFP) and this is difficult to do without losing lean muscle mass as well. Basically I don't want to lose any more weight overall (in fact I'd be happy to put some on!) but I do wish to further decrease my BFP and the last few ounces of body fat are frustratingly stubborn!

I believe I have my training right. i.e. 4 x 45 minute high intensity aerobic / resistance circuits per week. As well as 25 minutes cycling to and from work 4-5 times per week, plus other sports and remaining generally active.

My diet is low GI and typically consists of porridge for breakfast, large amounts of fresh fruit all day. 3 slices of granary bread with protein in the form of meat / fish / peanut butter at lunch. At night a high protein (meat or fish) dinner with a fresh vegetable stir fry and no further starchy carbs, and I don't eat at all after 19.30. I usually eat small amounts at least every 2 hours made up of 3 fairly small main meals and snacks in between. Also drink lots of water and cups of tea!

I allow myself 1 meal of whatever I like per week which would typically be a curry with naan bread and rice ( I have been told that a carb blast like this once a week is a good thing anyway??). Generally have 2-3 alcoholic drinks a week.

Can anyone offer any advice on how I can improve this to get leaner. Maybe I am kidding myself and I've got it totally wrong?! So please be brutally honest if you think that is the case!

Hope you can help.
Thanks for reading. Dan