endurance road bike for new starter

I'd say that anyone of these bikes would do the trick: https://www.bikejungle.com/bikes/road-bikes?pfen=500&pten=1200

Why not the CAAD Optimo with disc brakes?

As others have said you need to start forming your own opinions and try a few out. You may find that you don't actually like the ride of a bike you 'wanted'.
If you buy the bike that puts the biggest smile on your face after a test ride you'll ride it more.

If it fits you can't go too far wrong with one of these.

Has mudguard and pannier rack fitments, steel frame so not mega light but robust and an easy fix if you drop it

Use topcashback and get another £13 off the already silly low price. https://www.rutlandcycling.com/bikes/road-bikes/return-marin-four-corner...

Rutland and other places have lots of bargains, in all honesty I'd avoid getting either of the two bikes you mention, boring as and low spec, basically getting £150-£199 frameset with £350-£400 value put on the lowest spec Shimano road group (with even cheaper replacement parts in some cases), cheap wheels and basic finishing kit but with a big brand name.

You want bargain basement that will still do a job for you https://www.decathlon.co.uk/triban-500-se-road-bike-id_8306187.html

I'm not sure you necessarily need an "endurance" bike...

To be honest, at the lower end of the price range - there really isn't the scope to distinguish bikes apart much.

There aren't particularly significant performance differences between the cheaper bikes. I've never heard of Corratec.

Do you know anyone whos int cycling who could help you buy second hand? That'd allow you to get a good deal. If you are looking to take up cycling more seriously, you'll very soon be wanting a higher quality bike than things like the Trek 1.1 and Giant Contend.

I think you need to engage a little more in the thread you created.  I would go along and try a few bikes and buy the one you can afford and is comfy

Or www.paulscycles.co.uk discount last years bikes. 

https://www.decathlon.co.uk/triban-540-road-bike-105-id_8350480.html?utm...

Tyres are not the best but conti 4000s are £30 each if you want to upgrade straight away, or just ride it as it is for a bit and see how you get on.

11 speed shimano 105

mavic aksium wheels

diesnt get much better than that less than 1000

If you want more road specific,  Decathon's triban series of bikes have good value but at the moment sales are on so you will also find many other brands discounted to clear space for 2018 bikes.

Dolan do good value & well regarded bikes too.  I would recommend buying from somewhere you can go to in person so that you can feel it out before you buy and also as most shops will give you a free 4 - 6 week first service to re-adjust anything that thst has bedded in from first use.  

The £250 Decathlon Triban 100 looks like an amazing deal:

https://www.youtube.com/watch?v=U4SxDfhM3cU

Or at £1000, Alpkits Sonder Camino Ai looks pretty good with either shimano 105 or rival groupsets

https://www.alpkit.com/spotlight/long-mynd-delights

Those bikes are so similar for a beginner I'm sure what ever you pick will be perfect for you. Go for the one you like the look of the most. Looks are the most important factor in a new bike. Everyone knows that!

Which Contend are you looking at? The 2?

https://www.giant-bicycles.com/gb/bikes-contend

Here's the Trek specs:

https://www.trekbikes.com/gb/en_GB/bikes/road-bikes/performance-road/1-s...

If you compare components (Claris v Claris models), they seem much of a muchness, apart from the Giant having a wider range at the cassette (better for hills). The stack and reach are similar too, with the Contend a few mm less aggressive (slightly higher stack) but at your age, if you have no injuries, that shouldn't make much difference and you may prefer the more aggressive Trek.

They're both bottom of the line models of major brands and you may get more for your money going for something less popular, or secondhand. Certainly, you could get something that would be less of a thief magnet. 

Second hand, spend about £300 on something someone purchased on a whim. If you ride it a hundred times it cost you £3 an outing, if you ride it 10 times and sell for £250 it cost you a fiver an outing to find you don't like it.

Alternatively, spend a grand and potentially lose 40% in a year if you don't enjoy it

Ummm, without telling us more about your background, it's not easy to say. Age, previous cycling experience, flexibility, where you intend to ride, budget...