Boeing 737-300's G-CELB/D/S will be withdrawn from service this winter. These will be replaced with further 2nd hand Boeing 737-800s which are been acquired as replacements.
A further 5 ageing Boeing 737-300's will be withdrawn next winter 2016 to be replaced by the new fleet like-for-like.
The current 11x Boeing 737-800s which are leased will then have there leases cancelled and be replaced like for like on delivery of the new aircraft in 2017. Once they have gone they maybe some growth.
The Boeing 757-200 fleet will all under go heavy mantanice this winter with some receiving the glass cockpit upgrades and will all be kept in service for at least another 5 years and maybe beyond.
Meanwhile Boeing 737-300QC, G-CELR has now been converted permently to passenger flights only due to less aircraft been required for the overnight royal mail contract even though it will keep its cargo door. They maybe others to follow as well.