Using charts from here http://fxtop.com/en/historical-exchange-rates.php, the price movements can be approximated back to 1968.
Prior to the drop in the late 60s it is represented as having wiggled around the 2.8 mark, shown at the top by the 2 red lines.
I've marked a few significant dates, one of which significantly, and possibly the most amusing, was
1. an article in the WSJ, April 1975, which ended, "Goodbye, Great Britain. It was nice knowing you." The article recommended the sale of sterling investments in the face of high taxes. (https://en.wikipedia.org/wiki/Pound_sterling, & http://www.wsj.com/news/articles/SB10001424052748704107104574570122315830890)
It appears the pessimism had effect, and the British Pound crashed against the US Dollar ,
2. making a then all time low of around 1.56 precipitating a crisis which had the UK government going to the IMF.
The Brent oilfield had been discovered in 1971, and at this time it was a problem of technology, not potential that impeded benefit …
3. November 1975 (3) that the first North Sea oil pipeline came online. (http://news.bbc.co.uk/onthisday/hi/dates/stories/november/3/newsid_2538000/2538155.stm)
4. November 1976 saw the first oil from Brent.
UK National Archives of Cabinet Papers: “By the end of 1977, partly as a result of new oil revenues, there were improvements in the balance of trade. Britain did not need to draw the full loan from the IMF.” (https://www.nationalarchives.gov.uk/cabinetpapers/themes/sterling-devalued-imf-loan.htm)
Optimism. The pound bounced back up to over $2.4.
Early 80s brought global recession, and under Paul Volcker, “Fed policy to aggressively target the money supply rather than interest rates.” By limiting credit and thus tightening money supply the combination of this, and recession is what helped the huge spike in the value of the US Dollar . (http://www.federalreservehistory.org/Events/DetailView/44)
The pound came very close to parity at the beginning of 1985.
6. UK North Sea oil production is reported to have peaked here at ~85m barrels per month – it wouldn't have been known at the time it was the peak … The Pound rose strongly again.
7. Black Wednesday, George Soros, the ERM etc., is recent enough history. The pair made a sharp drop / corrective b wave before …
8. The discovery of the Buzzard oilfield, June 2001, the biggest in the UK, & coincides with the start of a large upward impulse C wave …
9. “North Sea production reached an all-time dip of 17 percent within the past two years, the lowest since the 1970s.” April 25, 2013, (http://www.energyandcapital.com/articles/north-sea-oil-discovery/3322)
Over that period the pair remained suppressed, and just after buoyed by the transitory hope of higher interest rates in 2014, producing a relatively minor C wave.
May, June 2015 saw production fall to next to nothing. (http://www.tradingeconomics.com/united-kingdom/crude-oil-production). From what I can ascertain there are infrastructure age problems which if resolved could squeeze out more oil , but
a. given current oil price and consequent removal of incentive to do that, and
b. in that North Sea oil has been pivotal to optimism for the last 40 odd years and
c. in that the pair is hovering over such a critical at about 1.409…
d. the additional pressures of Brexit, the recent BoJ move etc. etc.
… it might be time to revisit at least in sentiment, “Goodbye Sterling, it was nice knowing you.”
(I hope to get a more detailed close up time frame chart published later - there appears to be some interesting levels)