Not saying that anything Seffie is saying is wrong, I just dont think he/she gave you all the options that you can choose from. So, you can listen to Seffie, or you can listen to me, just two different options, one isnt necessarily better than the other, it just gives you a wider perspective:
Is it possible to adapt this tank? ie
Lights would need replacing- is this as simple as new bulbs?
Skimmer?, where would this go?
2 heaters?
How much live rock and roughly how much would this cost?
Do i need a filter when using live rock and live sand?
Power heads to disturb the water surface? How many?
Lighting is a huge question because there is no one set answer for something as simple as, what light should i get? You should look into specifics, what coral EXACTLY would you like in your tank. There are two main types of lighting for reefs, and two minor types. The two main ones are Metal Halide and T5 High Output linear Fluorescent. These two are the most common, but each are almost completely different except for the fact that they both create light. I personally am a bigger fan of MH (metal halide) since I like how it uses less linear space and it has a more natural effect visually IMO. Look into the differences and choose between the both, if you are going reef. The two less popular for reefers is T5 power compact lighting, similar to T5HO linear lights but not as powerful, though the design can use less room, it is hard to get a good reflector and therefore not as good as linear T5s. Another option is LED lighting, LED can be more effective and powerful than MH and T5HO, but it is very expensive to get a good LED fixture that can out compete MH and T5HO. LED is also used in moon lighting which offers little more than aesthetic values. So, do a little research on all of these before you commit to something immediately, remember, this is your tank and you can do it the way you want, and there are many many MANY different ways of having a reef tank.
Different skimmers can go almost anywhere, and there are good skimmers in each category. There is HOB, which is what Seffie suggested, but there is a lot more options than just HOB and Deltec MCE, while the Deltec HOB might be the best, there is also the AquaC HOB which uses a different technology, but AquaC is American and I am not sure if it sells in the UK. There are also in tank skimmers, Tunze being an example, in sump skimmers, which are the most common, and IMO the best for the money, in sump recirculating skimmers, and out of tank skimmers, which are normally the largest, most expensive, but the most powerful ones. And if that wasnt confusing enough, there are many different ways a skimmer works, there are Venturi, Venturi Needlewheel, Downdraft skimmer, Air Induction (or something by that name), air powered, and there are probably a few more that i cant think of at the moment. So there are many more options than a HOB Deltec MCE skimmer that, in America at least, seems like an incredible waste of money. The skimmer i went with was a Euro-Reef RS-80, cost me 100 dollars second hand and since it is an in sump skimmer it can be much bigger than a HOB skimmer and much cheaper, therefore IMO it is much more effective than a Deltec MCE, but it does require a sump, and the Deltec MCE may be the smallest bit more reliable, at a MUCH higher cost.
For heaters, it depends on your room temperature and how much excess heat is given off by tank equipments (pumps give off heat). I rarely use a heater, and if I do its a 150 watt in a 80 gallon total water volume tank just to keep the temp in the 80s. Contrary to some beliefs, unstable temperature IS natural and is arguably beneficial.
Im not sure about rock and sand, because how many kilos of rocks in how many liters of water, well as an American I have no idea what it is unless i do some calculating, which wont be necessary as there are more UK members here
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No need for a filter, although mechanical filtration is a great thing to have, but you'd have to clean it a lot otherwise it could be counter productive.
Powerhead is like lighting, we need to know what you want before we can say what powerheads and how many, if all you want are some fish and maybe some basic LPS, 10x-20x would be fine, if you want a full on SPS reef you may even be looking at 50x or a bare bottom 100x water turnover. I would suggest a wavebox, Tunze wavebox more like, but it is expensive, if not, koralia pumps or tunze stream pumps are good. Stay away from impeller pumps, you want propeller pumps.
Lastly I dont think sumps are getting good enough treatment on the UK side, maybe its just the members on this forum but here in the US, sumps are practically a life line on many tanks, it is rare for people to have a tank above 30 gallons without a sump, unless they didnt know what they were doing. With sumps you can get bigger and more powerful skimmers for a cheaper price, you can hold a large refugium, you have a large amount of water capacity for more stocking or just dilution to play things safe, you can keep your reactors in there, your heaters, its much safer to dose in sumps, most calcium reactors are made for sumps etc. I HIGHLY suggest a sump, they are very easy to plumb into your main system, and once plumbed they are basically part of your tank and you dont need to give it extra care, unless you have a fuge, then you all you would need to do is add a light.
I know this is much more complicated than what Seffie said, but I've given you a lot more options for you to choose from, now instead of doing what someone says you can choose what YOU want to do with YOUR tank. Hope this helped.
aboard, so you have 46 uk gallons there 
lol
