loosing 5kg in 3 weeks?

5kg of bodyfat = 38,500Cals.
You'll need a daily defecit of 1833Cals for every day of your 3 weeks to achieve that.

It's not possible in any kind of healthy way - in my opinion.

Opt for 1.5kgs and you'll achieve it and maybe slightly exceed it and you'll notice the difference for sure.
Try something like 1833 daily defecit and you're more likely to crumble after 4 days and ultimately achieve nothing.

If I had a target of 3 weeks I would use that to motivate myself to work harder than usual. A great way to loose weight quickly is spinning! It can burn up to 600 cals per class (obviously this depends on your weight). Try this 4 times a week. In between I'd do some toning classes like Pilates to help with inch loss.

i wouldn't drop below 1200 cals, you need to be healthy and eat well if you up your exercise. I think to get anywhere near 5kgs you'll need to do some serious cardio. Try dvd's too so that you can get extra workouts done at home Have a fab holiday!

Someobe told me to cut out carbs, but Im not sure if ill survive without my morning porridge??!

What that will do is deplete your body of glycogen stores and with it as much as 2 kilo's of water. You weight will temporarily go down but it won't be fat loss at all.

This is what fighters do in the day running up to weigh in, though they go more drastic and add in salt baths and sauna's. They drop 7kg in a week then put it all back on after weigh in before the fight. There's nothing healthy about it at all