Off topic a bit,
a year ago I made the same trade, and the Honda dealer offered me considerably more for the Tiger against a new CT than the Triumph dealer offered against an Explorer. And the CT is a much better bike than the Explorer IMHO.
However, I rarely worry about the trade in offers, or the price on the bike but consider the cost to change, that is how much do they want off me ? Ask the same question against cash or the difference finance packages.
Even if you have the cash, a finance package can be a better deal, and you can always clear the finance after you've got the bike.
You ask about the price of a one year old bike, but it's worth exploring the option of new, especially if you are financing as the deals can make a new bike cheaper than a second hand one. Also, check to see if the service plans are still been offered against new bikes, this can equate to 70-1000£ saving in real money over 3 years if you intend to have the machine dealer serviced (even independents can't really compete with £500 for four services)
At the end of the day, what you pay isn't important, what's important is that you are happy with the deal and can afford it. However, probably worth looking at other bikes in your area and gauging if it's a fair ticket price. Pre-loved prices vary over the country so a fair price in the North might not be comparable with a price for a bike in London.