On the outside only the door handles are shared with the Astra 5dr hatchback, while there are steering and suspension changes that make the GTC more fun to drive. In all, it's enough to make the GTC a convincing alternative to sporty coupes such as the Hyundai Veloster and Volkswagen Scirocco.
Here's our guide to buying the best Vauxhall Astra GTC.
Which engine should you go for?
The Astra GTC is available with a range of turbocharged engines. The entry-level 1.4T petrol model has 118bhp; it's eager enough, but a bit weedy for a sporty car like this. You're likely to feel short-changed.
The 1.4 T 180 petrol engine is our favourite engine in the GTC range; lesser petrol engines are rather weak.
For a few hundred pounds more, there's a 138bhp version of the 1.4T. Fuel economy and emissions are the same as the lower-powered version's, but there's no extra torque, so it's barely any quicker. We think it isn't worth paying more for.
If you want performance to match the looks, the 177bhp 1.8T petrol engine is the one to go for. Once the turbocharger gets into its stride it provides near-hot hatch pace. It's our favourite engine in the range.
It's a big step up to the Astra VXR, which has a turbocharged 2.0-litre engine that develops 276bhp. It's quick in a straight line, but the VXR struggles to deal with putting so much power through the front wheels the tyres and steering are too easily overwhelmed through corners.
The diesel engine line-up kicks off with a 109bhp 1.7. It's very frugal, but runs out of puff too easily. There's also a 129bhp 1.7, which is stronger, but still rather gutless.
The 163bhp 2.0 CDTi diesel costs only a few hundred pounds more, and it packs a much bigger punch, without using much more fuel. It's a shame it's so noisy, though.
If that's not enough there's the 2.0 Biturbo, a twin-turbo version that develops 192bhp. It's quicker still, but there's too high a price premium for it.
Which trim should you choose?
The Astra GTC is available only in sporty trims: you don't get the more basic versions that you do with the Astra hatchback.
As a result, standard equipment is pretty generous. Even entry-level Sport models come with air-conditioning, 18-inch alloy wheels, a DAB radio, a USB connection, stability control and six airbags.
There's a premium of between 1225 and 1410 for SRi trim, which adds sports front seats, automatic headlights and wipers, front foglights, an electric parking brake, Hill Start Assist, a front armrest, three-spoke leather-trimmed steering wheel, front door sill covers and dark-tinted rear windows.
That's a decent amount of extra kit, but we think it would be wiser to go for a Sport model and add a couple of choice options.
Biturbo models come in a bespoke trim that makes the GTC sportier, but very expensive. The cosmetic makeover features a different bumper and front grille, side skirts, a body-coloured rear spoiler and twin stainless steel exhaust pipes. There's a sportier steering wheel and pedals, while the suspension is lower and stiffer.
Astra VXR models have an even bolder makeover, and extensive changes to the steering and suspension that turn it into a hot hatch worthy of its lofty 26,995 price. They get the same comprehensive standard of kit as Biturbo models, but have upgraded interior trim and front seats.
Which options should you choose?
If there's one option we'd definitely recommend for the GTC, it's parking sensors. Rear visibility is pretty poor, so it'll be money well spent to avoid parking scrapes.
Front and rear parking sensors are a 385 option for Sport and SRi models, while rear parking sensors only are a 195 option for Biturbo models, which have a different front bumper.
The 230 Sight and Light Pack is definitely worth adding to Sport models it includes automatic headlights and wipers, which are standard on higher-spec models.
Many buyers will be tempted to upgrade the GTC's wheels, but we don't think it's worth it. Even the cheapest version comes with 18-inch alloys that fill out the wheelarches nicely. The optional 19-inch or 20-inch alloy wheels look great, but add a firmer edge to the ride.
Adding a panoramic windscreen gives the GTC a unique look, but it's not cheap at 850 and, because it's not to all tastes, it could make the car harder to sell on.
Think carefully before choosing the optional satellite-navigation system, too. It's rather fiddly to use and costs 855.
Vauxhall Astra GTC 1.6T 180 Sport 20,765
Light and Sight Pack 230
Front and rear parking sensors 385
Total price 21,380
How to haggle for a Vauxhall Astra GTC
Vauxhall showrooms are happy hunting grounds for discounts and there's no exception for the Astra GTC. You won't quite get as much of a discount as you would on an Astra hatchback, but haggle hard and you should be able to negotiate at least 2000 off the list price of all but the VXR.
Discounts on the VXR are harder to come by, although you should still be able to get around 800 off the list price.
Maximum you should pay for our recommended Astra GTC 19,025 (including options)