2 years ago on TV there was a series called "Hitler's England" or Britain, I think. I believe it was based upon a book using recently released Secrecy Act files including some startling Churchill statements.

For example.
According to it, Churchill was willing to violate the Geneva Convention on Bio-chemical weapons and bombard the invasion beaches with Nerve Gas/agents.

But it also went into the conventional plan and lines of defenses.
It even mentioned that in the real war alot of the British gov't and national treasures had already been transferred to Canada where a new UK Parliament would operate from. The Crown already had its own residences but it went into interesting detail.

Though the series went on to assume that even with the Nerve gas used, Britain would be occupied. Then it went into the Resistance movement.

Does that help?
Anyone confirm the name of the book or series?

Correct i saw the series and the biological weapon of choice was Anthrax and Churchill authorized that in the event of an invasion vast quantities of Anthrax would be released along the invasion front. Churchill was fully aware of the civilian casualtie that would eventuate and the political fallout within the populace but was willing to doo all that was available to Britains survival.

And also that the Series did in fact convey that secret British document stated that Britain could not hope to hold off an invasion had the Germans had launched Operation Sealion. Mainly due to the fact that the RAF was running out of trained pilots if the Germans had kept up the pressure on the RAF for two weeks more then the RAF was a spent force, plenty of planes but no one to fly them.

And also i think i have read that the RN heavy units (Battleships, Battlecruisers and Aircraft Carriers) were indeed expressly forbidden to be used in the role of Invasion Fleet interdiction, they were to be expressly used in the transferrence of Royal and Government members and assets to Canada.

They did give the signal Cromwell on Sept 7th 1940... Oops!

September 7th 1940

The signal for this alert is "Cromwell", a code name that was used only by the Army. And one of those Army battalions that were alerted was the 18th Australian Infantry that was based at Amesbury Abbey. The report came through at about 9.30pm. The 18th Infantry Brigade was at this time, only at about half strength because half of the brigade was on leave, many of them now trapped in London because of the bombing. But was hard to keep such a secret, church bells started to peel, road blocks were set up and even plans were put in place for the blowing up of some of the bridges.
For those that were on duty, they were told to stand by for an immediate move. By midnight, no further information or orders had been received so the men were allowed to return to their billets, but were to be prepared to move at one hours notice should the invasion be confirmed.

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The Royal Navy call sign equivelent to the Army's CROMWELL Alert was "Blackbird". This was the signal that the German invasion fleet was sighted, identified and inbound. All Royal Navy warships within reason were instructed to return to the nearest RN base ASAP, re-fuel, re-arm and make ready to do battle against them in the channel. This meant that RN destroyers would abandon their convoys and make a mad dash back to base to re-arm and re-equip.

No.
Anthrax was never considered for use against any invasion force, just Mustard gas.
Again no.
There was no realistic way the Germans could hope to protect the invasion fleet from being sunk by the largest navy in the world at that time, the RN.

Guess what Its another No.
On the date of the switch to bombing London the RAF had more operational single seat fighter pilots than the Luftwaffe. The shortage of pilots Dowding was worried about, were experienced Squadron and flight leaders.

Must admit, I'm getting a little fed up with using this word
No, they weren't forbidden, its just that the RN didn't plan to use them. They considered the 20+ cruisers, the 50+ destroyers, and the hundreds of auxiliary craft were enough to deal with any invasion force
Ho Hum
No, they weren't

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if in doubt....Panic!!!!

If the Royal Navy didn't intend to use "heavy units" to interdict and destroy the incoming German Invasion ships, then why did they send a large portion of the fleet to more southerly ports like Rosyth, instead of keeping them safe and away from harm at Scapa Flow?

Didn't the 'Royal Oak' and Prien have something to do with the decision ?

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"Stand by to pull me out of the seat if I get hit" - Guy Gibson

The sinking of the Royal Oak was much earlier. By 9/40 the blockships and defenses at Scapa flow had been added-to and markedly increased. Moving the Fleet South was as a result of the Germans preparing to make Sealion a reality.

I guess it was up to the RN then (?)

From " The last ditch" by David Lampe:

"So few military vehicles had been brought home from France that the few mobile defence units that could be raised in the summer of 1940 had to rely on hired civilian motor coaches for their mobility. Eight hours´ notice was needed just to get these units on the road- more time than the first wave of Hitler´s invasion armada would have taken to cross the English Channel and unload its troops. The defence units would then have crept across the country very slowly, impeded by the absence of signposts."

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By September the date of the planned invasion, the equipment situation for the British army units defending Britain had improved quite considerably, as this post from the American poster RichT090 on the Axis History forum shows

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if in doubt....Panic!!!!