You could just ‘eyeball’ it and look at the answers: something from the southwest at about 60 knots.  

Or you could average the winds shown on the chart:

            Just after departure                                                          230ºT/95

            At 005ºE                                                                               230ºT/55

            Approaching London mean of 245º/35 & 220º/40 232ºT/37

                                                                                                Mean 230ºT/62