The first thing to mention is the fact that all £2 coins, whatever the design are worth £2.
That said, a coin collector, such as someone looking to add to or complete their "Great British Coin Hunt" collection, may be willing to pay more than face value.
Realistic prices for circulated (but in good condition) collectible £2 coins would normally range from two to six times face value. Actual value to a given collector will of course depend on the design (and how difficult it is to find) and condition of the coin.
When valuing a two pound coin, scarcity is key - as at today, what are the chances that this coin will appear in my change.
This of course depends on the total number of £2 coins in circulation and the total number of your target coin in circulation.
It is not possible to know exact numbers, but we know it cannot be more than the number produced (coins made for circulation, so excluding Royal Mint brilliant uncirculated versions) - and will likely be much lower due to coins already in other people's home collection and lost or damaged coins.
Popular and interesting designs are more likely to be held in home collections, so these designs become increasingly hard to find in circulation.
Year of issue is another factor to consider, older coins have had more time to be taken out of the circulation pot, so can be hard to find. Coins that have remained in circulation for a long time, may well be in poor condition, with designs rubbed down, marks, dull colour etc. A collector would want a coin in good condition, so this helps push up prices for older coins that were removed from circulation by another collector.
Scarcity leads to additional demand, which in turn creates a price point for each coin.
To help you determine a fair value, see the £2 coin valuation table which shows an expected sale price range based on recently sold circulated coins.
Note: Some examples of coins that are in excellent or uncirculated condition, could achieve higher values. You should also consider all other factors refered to in this article when determining a fair price to buy or sell a coin.