How does the dopamine spike from drugs compare quantitatively to pleasurable non-drug activities?
This review article [1] gives dopamine responses for rats (similar to the BBC article above) and includes references to the underlying studies:


Sex/Food:  150% - 300%
Alcohol/Ethanol:  190%  (1g/kg) * 
Morphine: 200% (1mg/kg) *
Nicotine:  220%   (0.6mg/kg) *
Cocaine:  350%  (5mg/kg)
Methamphetamine:  1000%  (1mg/kg)


These are percentages of the baseline dopamine level (not percentage increases), so 100% would be no effect.  They correspond to dopamine levels in the Nucleus Accumbens, which is a brain region involved in processing reward.  

Also, the drug effects are dose dependent, so the above values show the dosage with the largest effect among the dosages tested in this study [2], which was referenced from the review article.  The values marked with asterisks were estimated visually from the graphs.  

[1] Allerton M, Blake W. The "Party Drug" Crystal Methamphetamine: Risk Factor for the Acquisition of HIV. Perm J. 2008;12(1):56–58. 
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3042341/

[2] Di Chiara G, Imperato A. Drugs abused by humans preferentially increase synaptic dopamine concentrations in the mesolimbic system of freely moving rats. Proc Natl Acad Sci U S A. 1988;85(14):5274–5278.
 https://www.ncbi.nlm.nih.gov/pubmed/2899326