Brick up wall between 2 rooms ~ Bricks or Blocks ?

French doors connect the dining / living room which I'm going to revert BACK to a solid wall (the rest of the wall is 3" x 9" commons) but I'm unsure whether to go for reclaims, medium density blocks or aerated (wickes) blocks. If the latter do they require special "tile type" adhesive or just normal bricklaying mortar. Also should I "key in" to the existing brickwork or will a "wall starter" top to bottom both sides be sufficient to prevent any movement / cracking?

Old reclaimed bricks might be easier for you to bond in to the existing brickwork, and are easier to lay.
Blocks can obviously go up quicker, but the dense concrete (7N) blocks are heavy. The aerated conc blocks are much lighter and easier, but the shrinkage is greater than with the dense block, and you may find a small crack opening up where new meets existing.
Personally I'd go for brick.

Thanks Tony, would you advise removing the odd 1/2 brick in the original wall to key in the reclaims, or is a wall starter acceptable.

Definitely brick for the above reasons and if you have half bricks in the existing sides it should be easy enough to loosen the mortar around them, tap them out and re-fill by tying in the new brickwork. Will be a much stronger bond than using wall starters.