sorry mate but a 1.2 isnt going to give you a massive return on your money.
is it your first car ? if it is one idea might be leave it the now and wait a year then see what your insurance does. if it does see what a 1.4 or 1.6 does to you.
if you do want to stick to this car just know. a panel filter and exhaust will give you a couple of bhp but dont look for more than 5 or 6. DONT touch induction kits although you might gain a couple of bhp at the top end you have a big chance of losing power and torque through the mid range.
fuel pressure regulators ( power boost valves FSE valve whatever you want to call it ) will give you a more responsive throttle, maybe a little power.
cams will also give you more power but these might be a little outo your price range. if you do go for them stick to a fast road version. stay away from race these will struggle to hold a steady idle.
hope this helps but like a say even with that you might only get 15-20 bhp from it all, if your lucky.
you also have the option of remapping (chipping if its an old car normally pre 2000) but again on a 1.2 you might only get 6-8bhp for £300