For the sake of £50 get a new one via your insurance, make the crack worse! lol
Most autofactors sell a kit u can buy and do it yourself, but again all depends on how bad it is, 2cm may not sound much but may be enough. Places like autowindscreen etc can do it via your windscreen cover on your insurance also.
dont they (some kind of windscreen place ) do what called silicon filling on the screens better than a hole new screen coz it dont touch your insurence and its abou 40-50 quid and up to tree fills i think