You need to talk with a tax-accountant for this one.
But first, even in these times, is e40k a bit low ?
On the other point, your main point, CGT is at 25% on what could be called the 'profit' (not the correct term but it'll do for now). This 'profit' is the difference between the sale price and the price you bought it at. Instead of the ourchase price, if you inherited it - it was the market-price then of the site.
If the site is part of a much larger field, you need to apportion it. If it is part of your garden, there are reliefs available - you need to discuss this with a tax-accountant who can have full access to the facts.