A paper handling apparatus comprising: - a plurality of feeder stations (A, B, C, D), for feeding documents to a conveyor (4, 60), - means for collating documents into serially travelling packs; - means for collating said serially travelling packs (61 - 65) fed by said conveyor (4, 60) into groups of documents, characterised by - an inserter module for inserting each group into an envelope, said inserter module comprising: - an envelope hopper, - an insert pawl for pushing a completed collated group into the envelope - a wetter wherein the flap of the envelope is wetted, and - an output module where the envelope flap is sealed and the envelope is prepared for mailing, said paper handling apparatus further comprising: - means for monitoring the cycling and working times of sections of the inserter module, - means for determining at least one of: - a first desired gap being the minimum gap between the trailing edge of the last of serially travelling packs (61, 62) to be collated into a group and the trailing edge of the last of serially travelling packs (63 - 65) to be collated into the following group; - a second desired gap being the minimum gap between the trailing edge of one pack to be collated into one group and the leading edge of the following pack to be collated in the same group; - a third desired gap being the minimum gap between the trailing edge of the last of serially travelling packs (61, 62) to be collated into one group and the leading edge of the first of serially travelling packs (63, 65) to be collated into the following group; and - means for controlling at least one of the feeder stations (A, B, C, D) to achieve at least one of the respective desired gaps (101, 102, 103), wherein the first desired gap is controlled in dependence upon the slowest cycle time of any one of the wetter, the output module, the envelope hopper and the insert pawl track. - a plurality of feeder stations (A, B, C, D), for feeding documents to a conveyor (4, 60), - means for collating documents into serially travelling packs; - means for collating said serially travelling packs (61 - 65) fed by said conveyor (4, 60) into groups of documents, characterised by - an inserter module for inserting each group into an envelope, said inserter module comprising: - an envelope hopper, - an insert pawl for pushing a completed collated group into the envelope - a wetter wherein the flap of the envelope is wetted, and - an output module where the envelope flap is sealed and the envelope is prepared for mailing, - an envelope hopper, - an insert pawl for pushing a completed collated group into the envelope - a wetter wherein the flap of the envelope is wetted, and - an output module where the envelope flap is sealed and the envelope is prepared for mailing, - means for monitoring the cycling and working times of sections of the inserter module, - means for determining at least one of: - a first desired gap being the minimum gap between the trailing edge of the last of serially travelling packs (61, 62) to be collated into a group and the trailing edge of the last of serially travelling packs (63 - 65) to be collated into the following group; - a second desired gap being the minimum gap between the trailing edge of one pack to be collated into one group and the leading edge of the following pack to be collated in the same group; - a third desired gap being the minimum gap between the trailing edge of the last of serially travelling packs (61, 62) to be collated into one group and the leading edge of the first of serially travelling packs (63, 65) to be collated into the following group; and - a first desired gap being the minimum gap between the trailing edge of the last of serially travelling packs (61, 62) to be collated into a group and the trailing edge of the last of serially travelling packs (63 - 65) to be collated into the following group; - a second desired gap being the minimum gap between the trailing edge of one pack to be collated into one group and the leading edge of the following pack to be collated in the same group; - a third desired gap being the minimum gap between the trailing edge of the last of serially travelling packs (61, 62) to be collated into one group and the leading edge of the first of serially travelling packs (63, 65) to be collated into the following group; and - means for controlling at least one of the feeder stations (A, B, C, D) to achieve at least one of the respective desired gaps (101, 102, 103), wherein the first desired gap is controlled in dependence upon the slowest cycle time of any one of the wetter, the output module, the envelope hopper and the insert pawl track.