I should preface this response by saying that I've set more than my share of ceramic wall tiles, but have yet to set a single ceramic floor tile. However, I'm familiar with the issues that need to be addressed in both.
I'd contact the places that retail ceramic tile in your area and ask if they use a cement board or wood for the tile backer.
Here in North America, the advice generally given is to never tile directly over wood of any sort, even exterior grade plywood. The reason why is that wood swells and shrinks with changes in it's moisture content, and the grout lines of ceramic tile simply don't have the elasticity to accomodate any such movement.
What we do here instead is use a dimensionally stable material (like cement board or a gypsum based tile backer panel like Dens-Shield) over the wood. That way, if the wood gets wet, any movement in the wood will be accomodated by the twisting and bending of the fastners holding the tile backer down to the wood, as well as any crushing of the tile backer by those fasteners. But, the tile backer itself is dimensionally stable, and any movement of the wood below it will not translate into tensile or compressive stresses carried by the tiling or grout lines above it.
However, putting down cement based tile backer panels won't increase the rigidity of the floor as much as putting down plywood will, and rigidity is also important in ensuring the grout lines don't crack due to any bending of the floor when you walk on it.
Also, should the retail tiling outlets tell you it's fine to use wood as an underlayment over which to tile over, I'd definitely use plywood instead of chipboard. Plywood is much more rigid and would reduce any bending of the floor more than chipboard would.
Also, chipboard behaves much like a good breakfast cereal when it gets wet... it swells up and loses all it's strength. That's not what a good tile backer should do.
PS:
Regarding the gaps to be left between sheets of T&G plywood. Yes, leave the gaps.
You see, wood cells are shaped like long narrow cylinders that are closed off at their ends. As wood dries out, the cells walls become both thinner and stiffer, and this results in the wood shrinking considerably across it's grain, but by very little along it's grain. Lumber that's stamped "Kiln Dried" only means that the moisture content in the wood has been reduced to 19 percent or less. In a house, the moisture content will be less than 16 perecent. As a result, the lumber you buy will generally shrink as the water evaporates from the wood.
However, plywood consists of thin wood sheets that have been glued together, and the glue bonds better when the wood is dry. Consequently the plys of plywood are dried to a moisture content of only 4 percent before being glued together. And so, once you install that plywood and it absorbs moisture from the air in your house, it is much more likely to swell and expand than shrink and contract.
That's why they recommend leaving a gap between panels when installing plywood, but you also hear that the wood joists and wall studs in a new house will shrink as they dry out.