Air carrier First Officer reported a traffic conflict when lining up for takeoff behind another transport aircraft with minimal distance at an international airport. The First Officer indicated the aircraft was subject to jet blast and uncommanded movement due to the proximity of the other aircraft when power was applied for takeoff.

Narrative

Prior to this event we had two maintenance occurrences; the first maintenance event took place 10min prior to push back; our IFE (In Flight Entertainment) was not working. After the issue was successfully resolved and few minutes past departure time; we called for push back and engine start; unfortunately London airport was doing a Runway change and we waited for another 35 min or so until we pushed back. Once we disconnected from tow bar and finished starting engines; we saw a STATUS MSG ' NOSE A/G DISAGREE' ; making this our second maintenance episode. We called Dispatch and Maintenance Control via satcom and were able to resolve the problem; then coordinated with Ground Control to taxi for few feet and verify that our STATUS MSG will not repeat. After all this procedures were completed we waited for another 15min or so before we could get the Maintenance Release and finally complete our respective checklist. Finally we called Ground for taxi; and we were told to continue to Runway 27R; then Tower instructed us to line up and wait behind the departing Aircraft Y. Aircraft Y was taxing in front of us (Right to left at medium fast speed) and entered the Runway; we followed it and executed Tower instructions however Tower informed Aircraft Y that another aircraft will be departing from a further down intersection prior to their departure. At this point we already entered the runway and our distance was getting closer to Aircraft Y in front of us; the FO and myself mention to the Captain that we are number 3 for takeoff; but it was to late already. The distance between us and Aircraft Y was minimum; the Captain tried to slow down to keep momentum and finish the turn of our plane and be fully lined up; unfortunately is at this point when we noticed that Aircraft Y in front of us was executing a static takeoff and their engine jet blast pushed our aircraft backwards few feet. The Captain compensated this and finally were able to get the space needed to finish the turn and get ready for take off.