Carbon or Aluminium

As far as frame material goes, really try to ride some different bikes and see how you feel about them.

If you're doing cycle to work you generally have to pay full price for the bike.  So a heavily discounted carbon frame may not be an option through cycle to work.  However, this means that alternative finance on a heavily discounted bike might be better value.  Good luck!

Dolan? Good bikes. Theres a L'Etape 105 for 899, no admin fee I believe.

At your weight you'd be fine with any frame material - carbon, alloy, steel, they're all strong as hell.  But if I were you I'd choose a metal frame, purely because I have a carbon bike and to me it just feels a bit soulless.  I like my bikes to "ting" when I flick them with a nail, not "dunk" as the carbon frame does.  That's why out of all my bikes, I ride the steel one the most often.

Have a good look at what Ribble Cycles sell, they do some cracking bikes at very good prices.  I still have one of their winter trainers from a few years back, it's a very quiet comfortable bike that can shift when you want it to.

one thing to be aware of with planetx is that they may charge an admin fee when using some cycleschemes.

Cannondale CAAD12. 105 and the best aluminium frame ever for a touch over the budget. Discs for a few dollars more but I'm not sure I'd bother.

Especially at your weight, 220 lbs,  go for a steel frame with wide rim 32 or 36  rounded spoke wheels that can take a 32mm tire inflated to 70-85 psi, get a leather saddle, don't cut the stem, and enjoy a comfortable daily ride.   Your >average< carbon bike with racing wheels is made for someone weighing 140-160 lbs.  

I've got a Giant Defy 2, real quality aluminium frame with carbon forks which is really comfortable and is my everyday ride to work/winter bike, fairly quick, first road bike I bought and is always a joy to ride. I've done plenty of century/long rides on it and always been comfortable. I also have a 2015 Cannondale Supersix Evo which is all carbon, nice light-ish wheels (upgrade from the crappy Fulcrums that came with it), SRAM Rival 11 speed (apparently same level as 105, but lighter). The Cannondale was originally £1,700 but I saw it online in September for £1,049 and I got it on the cycle to work scheme. All I had to do was 'top up' the cyclescheme voucher.  Did the same previously with a Planet X Pro Carbon which was another great bike, fun to ride, but not in the same bracket quality wise as the Cannondale. Out of the two I have now, the Cannondale wins hands down in every aspect, stiffness, comfort, weight, looks, speed. The weight is currently 7.5 kg with scope to get lighter, which I think is not bad considering the price! I knew straightaway on the first ride, it just feels like a quality frame, really plush ride. I guess my point is, if you look around you can get a brilliant frame for around £1,000 and use your cycle to work voucher. The wheels at that price will generally be not the best, but you can upgrade bits later. Seems September time is when the next years new bikes start coming in so thats the best time to have a look. Personally I wouldn't get a carbon bike that normally retails around the £1,000 price again. I'd only go for it if it's been heavily discounted like the Cannondale. 

I've got one of each. The carbon bike is a boardman road team carbon, the aluminium is a Canyon Ultimate Al Slx (built myself from the frameset) . I think the boardman has a slightly more comfortable ride, but I prefer the Canyon overall. The canyon fits me better and the new 105 5800 I installed is much nicer than the old tiagra on the boardman. I'd always go for better overall spec and fit. Comfort is subjective, but both are fine for the longest rides I do (2hrs). If you're worried about crashing, get it insured. Most alu bikes have carbon forks, even replacing them and a wheel would be more than the cost of a policy and excess.

I purchased a Pinarello Neor from Halfords earlier this year under the cycle to work scheme. Aluminium frame with carbon forks and carbon rear triangle. Shimano gear throughout, including  105 shifters, but only Tiagra groupset. Listed as having basic brakes but mine came with Shimano to match. Am  15 st myself and works fine for me. Best compromise I could find, in partcular the Shimano wheels roll really well. Only thing I had to change was the saddle, which was too narrow.

What he said. Definitely go for an excellent alloy frame with a better groupset, than a cheap carbon frame and a fairly rubbish group as it would be for £999.

For your weight, I'd try for steel. Carbon would probably be fine but steel is bomb proof, especially at this price point, I just don't rate aluminium. I bought my steel winter bike on C2W scheme, it's only Sora but you've got an extra four hundred quid in the budget and I'm sure something exists somewhere with 105.

For that money you'll probably be better with aluminium, or steel.