I have an office-style desk, with a 25mm thick wooden top. I know it is fake-wood because there's edge trim around the lot. But its not enough surface area, so I wish to abut a "return" in such a way there is nothing to interfere with my legs/knees, so standing a 4 legged table to the side is not going to work for me.

I have a suitable small top, and purchased two kit legs for the outer end. That's all good. My question is how do I join them, for support and no exposed lip?

The new top appears to have thin strips of real wood as a veneer, but the core remains fake wood. There is a "wood-like grain" laminate on both faces.

The original desk has a top that can slide to the right by 100mm for access to a cable trough on the rear – so that grey metal bar has about 6mm of clearance to the underside of the top, and the top can be exposed to work on it.

Options for butt-joining the tops – The two tops should be co-planar and have no lip. A small recess is acceptable, from the corner chamfer. I suspect the rubbery trim would peel off acceptably well, but the wood veneer won't.

1. 
   Pocket screws – use some long wood screws at a slight angle, up from below so they terminate inside the original top.

2. 
   Some kind of metal plate below both pieces, screwed upward. Often called a "mending plate" or similar.

3. 
   Benchtop joiner kit- uses two circular recesses excavated into the underside of the top, and is then tightened.

4. To make removal easier, would two L brackets mounted back to back with a bolt through them be an option? Downside, nothing here holds the top of the edge closed.

5. Other methods I haven't thought of ?

Your thoughts ?