Base transfers vary in success from year to year. Right now, I reckon I could move to almost all other bases but expect a 737 type rating for the privilege.
Traditionally MAN & LGW have been the hardest to get into but that has changed more recently. I'd still hazard a guess at a year or two for LGW but MAN now joins all other bases and has strangely been under crewed for the past year.
The irony of the system is that we have recruited and sent all new blood to NCL and CWL as these bases are always under crewed but most moved out In the first bid round to places around the country including LGW.
I'm not sure I've really explained the system very well so I'll rephrase... We have a bid round on a regular basis, maybe every two months. At this time we can ask for a new base/fleet/command etc. Then in seniority order it is granted. If say I was at GLA which has a real short fall in FO's and wanted to move to LGW which might be 99% crewed I would still be successful in moving. A vacancy is a vacancy despite the situation at the base you have left.
On the flip side, if you are junior you could wait years for a vacancy at LGW as it matters not when he request was submitted. Even if you waited 5 years for a base move, if someone more senior to you requests what u want the day before the bid... He'll get it.
Hope that helps