They will pass with power fc cause they cant see it. If you have the hand controller make sure its not mounted above the dashline or floating around in the cabin.
How low is it? Could you fit a coke can under it? Most blue/pink slip places will pass for lowness anyway.
The main things they'll look at are...tyres, damage, rust, loose seats/interior, play in suspension/steering, bushes, oil leaks, coolant leaks etc.
I do regos at work so I could prob tell you most things they will/wont pass. Except we only do pink slips.
I can recommend a place for blue slip in bonnyrigg. Mate of mine works there. Will pm you the details.