Hi and welcome to forums and Airsoft in general, hopefully we can exchange plastic ball pleasantries one day.
In terms of getting started I would in your position hold off buying a gun until you get your UKARA, otherwise it would mean getting a two tone gun which whilst it may be good, it will always be two tone/ex two tone if you plan on selling it, remember its a lot of money to drop on a gun so you want it looking the best it can. Get the UKARA by playing 3 games over a period of more than 2 months at the same site, this is possibly the fastest way to get your UKARA, once you got, go on a shopping spree
You state that you only have £300 to spend, with that ill assume it means everything!
For your first gun definitely get an AEG NOT a GBBR, while GBBRs all have that realistic blowback action and recoil they are also more expensive to run and difficult compared to an AEG to repair. For a First gun i would recommend as other have done to get a G&G AEG, i would say stick to an M4 (AR-15) type weapon.
Depending on what you want the gun made of you can go for a G&G Combat Machine M4, most have the name starting with CM16 as model numbers such as CM16 SRL, the receivers (main body) of the gun is made from a strong polymer plastic but the rail is normally made from metal, they are cheaper and lighter but of course not made of metal. The model above is the GC16 series such as the GC16 SRL which is exactly the same as the CM16 SRL except that the receivers made from metal.
Example of CM16 SRL for sale at Zero One
http://www.zerooneairsoft.com/product_info.php?cPath=268_318_403_494&products_id=4397
Example of GC16 SRL for sale at Zero One
http://www.zerooneairsoft.com/product_info.php?cPath=268_318_403_496&products_id=5206
Recommended (and cheapest)
http://www.zerooneairsoft.com/product_info.php?cPath=268_318_403_494&products_id=5645
Above the CM16 and GC16 is the GT Advanced (AKA Top Tech Line), but in this territory its out of your budget, that said all the above guns function exactly the same, the gearbox (the working bits) are exactly the same as each of those guns, one will not perform better than the other just because it cost more, you pay more for aesthetics.
Also if you buy any of those new fangled G&G guns with the Electronic Trigger Unit (ETU) make sure you use an 11.1v LiPo, regardless of the horror stories you have heard of 11.1v LiPos destroying AEGs etc a G&G gun with an ETU will NOT function, while it might for a 9.6v Nimh it wont do for long as the battery drains, but is guaranteed with an 11.1v. Also regardless of G&G gun they are all built to withstand 11.1v LiPos, i have exclusively ran 11.1v Lipos in my G&G HK 416 and MP5 with no issues.
Lastly whilst i would say hold off before buying a pistol as they often dont see much use if your deadset on getting one i can only recommend you get one made by Tokyo Marui or TM for short, yes they are made in plastic and are limited to 280FPS due to TM being based in Japan and Japanese Law but trust me they are the best pistols out of the box, my TM M9 and TM FN-57 can range and even out range AEGs, failing that KSC/KWA is another decent brand, avoid WE like the plague. Also stick to common pistols, no point getting that awesome unique one when you cant find a holster for it. I have a TM M9, FN-57 and M1911, easy to find Blackhawk SERPA holsters for them, i also have a KSC M93R, yeah good luck finding a decent holster for it.
In regards to kit get a a decent pair of boots, lots of those can be had from various surplus stores across the UK, stay away from British Standard Issue boots as a large quantity had QA issues with rubber soles crumbling away, try and aim for Pro Boots or any made by LOWA as they are decent in quality.
Get decent Eye Pro, I cannot stress this enough, guns and kit be used and broken and replace but you only get once set of eyes, better not shoot them out, personally i use a pair of Revision Desert Locust Fan Goggles with Thermal Lenses (which annoying aren't available in the UK), the combination of fan and thermal lenses for me stops fogging.
Gloves, anything on your hands is better than nothing, Mechanix do a wide variety of patterns and colours for a fairly reasonable price brand new.
Clothes can be gathered as and when afterwards, nobody in Airsoft especially at skirmishes nobody cares if your are dressed like an elite operator out of Call of Duty or in t-shirt and jeans so long as you play fairly and take your hits.
Tactical Gear such as vests and chest rigs, go with what you like, just remember you are carrying it, i used to go all Assaulted vested up with helmet and battle belt, man i was finding it a hard time moving around in the summer, nowadays i just use a chest rig (much lighter) and battle belt to carry other miscellaneous stuff.
Comms: If you want a radio of sorts to speak to your bro get a normal (PMR 446) Motorola, they are decent enough for the job and as its a PMR446 radio you wont have to get a radio licence, if you decent to go all BAOFENG then you will need a radio licence, i dont know if OFCOM actively pursues people using them without a licence.
Lastly thing i would mention is Optics, dont bother with long range scopes for an M4 you are simply not go to have the range to use it, instead if you do want scopes consider focusing on red dot sights or the like. Personally i field a Real EoTech 551 sight (with lens protector of course), since using a real steel sight i find i cannot use fake EoTechs any more, call me an optic snob.
In summary
Get an AEG preferably a G&G CM16 or GC16
Magazines for the AEG
Batteries (11.1v Lipos)
Balance Charger (for 11.1v Lipos)
Get a good pair of boots
Eye Pro
Gloves
Tactical kit be it vest, chest rig or just a battle belt
Clothes in a pattern of your choice
Comms
Pistol you can decide to bump this up if you want but i would definitely go with TMs
Last rule of thumb, you get what you pay for, i personally prefer to get most of my stuff real steel if possible, its sometimes a false economy to get clone stuff, a clone M9 Blackhawk SERPA holster i had always allowed the pistol to wobble and one day it hit the mag release catch and drop the mag mid skirmish (i found it luckily after wandering the woods retracing my steps), a real steel Blackhawk M9 SERPA holster had no wobble and a clear cut out to avoid magazine release bumps.
. I was in the wrong position shooting or forgot to check my six before advancing, the guns worked well but I did not. Stil it is better to get stuck in than not. 
h34r: 
