Across:
   7. Nasty herb stings and smarts (10)
   9. India's politicians, devious fellows! (4)
  10. Topside roast initially carved with great authority (8)
  11. Rules for performing singer (6)
  12,22dn. Mary lets loose with words we can all understand (3 5)
  13. Steel used in autopsy chisels (5)
  14. First lady taken by the masculine French 21 (5)
  18. Leftward Peron take from all of country's leaders working together? (13)
  19,21. As famous movie fish, Mudskipper's number one in the big pond (5 3)
  20. Captive fish housing stank badly (5)
  21. see 19
  24. No change for 25 abused via internet (6)
  26. Removing toxins from bloodstream advisable? Yes, rinse regularly! (8)
  27. Stop and take back mouthful (4)
  28. Not taking direct path due to explosive mine danger (10)
Down:
   1. Smile about Peron having access, deleting the odd complaints (10)
   2. State making technology help humanist ends? (5)
   3. Leader performing mass at ten (9)
   4. Take over from principal leader after cutting short money lending (5)
   5. Whisk simple admiral away with every other 'character' in 6 18 24 8 (9)
   6. Frank work with English? (4)
   8. Chambers issue perhaps: bench, losing edge, help each one out of policy backflip (13)
  15. Heights of stormy violent sea (10)
  16. Breaks in trees holding listener in clutches (9)
  17. In this way, 21 is mad to recommend charges (9)
  23. Type of scheme involving some 21s being built and some geography drowned (5)
  25. Crooked line which runs through 2 (4)