have a look at the mcmillan pace calculator to get a predicted marathon time based on your HM time. The marathon time tends to be optimistic as its based on "equivalent performance", so I'd be recommend adding ten minutes to it for your first marathon.
The big benefit from mcmillan is that it will also calculate training paces for you.
PS It will also depend on the marathon you are attempting, you might want to add even more time if its hilly etc.
I’m not confusing net annual increase with total net immigration figures, I was trying (unsuccessfully) to illustrate a point. With figures of quarter of a million people and comparing it to a “small town every year”, it sounds like a large number. However when you compare it to the scale of the total population, it’s a tiny fraction.
To answer the original question – if we stop immigration, we are stopping 0.3% of the annual growth of the UK population. This will have no visible effect on the current contention for the national infrastructure. I would suggest it would be a timescale of circa twenty years until we saw a positive impact of this policy on the demand for housing/transport etc. The only way to alleviate this is to invest significantly more public money into the infrastructure, but there are strong political and economic reasons that prevent this.
If you dislike the quality of life in the UK then you are free to leave and live in any other EU country. It’s a bit more difficult to get into some other non-EU counties, but it’s still possible to legally emigrate to most of them. If you have some valuable skills (probably gained at very little cost through our public education system) that can be beneficial to the target country or the organisations based there, you may find it easier. We live in a global marketplace, which has many benefits but does require geographic mobility to underpin it.
We have a couple of hundred thousand immigrants, but what about all these inconsiderate people birthing children into this country and swelling the number of indigenous people! And I've read the Daily Mail, apparently these devious doctors (probably of non-english descent) have the audacity to keep the old people living longer! Its all Labour's fault because they didn't understand the consequences of the Tories entering the common market! Its a moral outrage!
We have an expanding population in the UK, which is currently around the 60m mark. 200,000 immigrants means that they have increased the population by about 0.3%. If our national infrastructure is so close to its limits, then I don't believe we can blame that 0.3% of the population.
I could look up the facts and figures on the number of births and the increased life expectancy of the "average" UK resident, but I don't TBH the original rant doesn't warrant the five minutes it would take.