As for using C5, A380, C-17 or B747, then transferring to a 'tactical' aircraft - that's precisely what the A400M is designed to overcome! It has the payload/range/speed of a strategic transport (but not the outsize capability of the An124, for example) - plus the characteristics necessary for a modern, rugged, tactical transport.
A tactical delivery by A400M from the UK direct to a destination in say Afghanistan or Iraq will take well over 10 hours to reach the destination and would require a fuel stop on the way. The crew would be exhausted by the time they had to carry out the tactical part of the mission. 
Taking the Iraq example, I suppose they could put a fresh crew on in Cyprus who would then undertake the tactical delivery to Iraq and return to Cyprus, but I suspect that the A400M would need to be air-to-air refuelled along the way back from Iraq to Cyprus and it’s going to be a long and tiring round trip for a tactical aircrew to undertake. I would have thought it would make a lot more sense to fly the cargo by strategic airlifter to a suitable base in the Gulf region, then use the tactical airlifters (C-130Js and/or A400Ms) to move the kit the last few hundred miles.
The problem here is utility. The Civvy freighter can't be unloaded without large specialized pieces of equipment (scissor lifts). It's confined to large airports with major taxiways and 10,000 foot concrete runways. Absent those things its utility declines to zero.
If there isn’t already that capability at the far end of the strategic air bridge, the simple solution to this problem is to fly the scissor lifts etc out in a C17. If you look at the major airlift operations carried out in the last 60 years by the RAF, there has almost always been a nice long concrete runway available in the general vicinity, and a safe enough distance away from the front line to mean that the strategic airlifters don’t need to be militarized to any significant extent.
In the 60’s the RAF used Comets, VC10s, Britannias and Belfasts to carry out the strategic airlift role. Then Beverleys, Twin Pins, helicopters etc to move cargo from the strategic bridgehead to the front line. Nowadays for the strategic airlift role, the RAF uses lots of “DTMA-rented cheapo civilian garbage” to augment their own Tristars, VC10s (both of which are obsolete) and C17s. As far as I know, the C17s are only used in the strategic airlift role, being seen as too expensive an asset to put in harms way (especially as they’re leased, not owned).
Why don’t the RAF lease or buy some modern, "bog-standard" commercial widebodies as FSAs (Future Strategic Airlifters) to replace the VC10s, Tristars and “DTMA-rented cheapo civilian garbage” in the transport role? There’s more than enough work to keep a fleet of new widebodies heavily utilised these days and they would require far less fuel and maintenance per tonne/km than the current fleet. I see this role as a completely separate requirement from the FSTA; FSAs would be far more efficient without all the plumbing and other mission equipment that are necessary for FSTA but unnecessary for FSAs. I’m sure Airbus in particular would offer a great deal on A380s, A330s or A340s at the moment. FSAs would be far more efficient at shifting the bulk of the cargo and troops than the fleets that are used at present. Much greener too. This would free the tactical airlift fleet and their crews to perform the tactical role they’re trained for rather than spending much of their time trucking up and down the airways. It would allow the VC10s and Tristars to focus on their tanking role until the FSTA arrives (the sooner the better). It would free the C17s to focus on shifting outsized loads and it would allow the RAF to cut down on the amount of “DTMA-rented cheapo civilian garbage” which goes thundering over BEagle’s house "at 0003 local, incapable of following the RW08 SID". 