Why is so that British girls are so keen to be pregnant?
I don't think they are. I think they just enjoy having sex, for the same reason many feamles here do.

Why is preteen sex so normal in Britain?
Are we talking about preteen sex or sex under the legal age? I would like to see some statistics to support your claim that it is normal. It may not be unusual, it may be on the rise but normal is another matter.

But to answer the question I think fashion and culture is probably the driving force. When you have rock star role models singing about sex and a fashion industry selling sexually provocative clothes, make up etc. etc. it is no surprise. Young people are very impressionable and considered not competent to decide for themselves (hence no vote) so is it not for those in power or with power to influence them in positive rather than negative ways.

Government pays the pregnant girls and families with single mothers.
This is where your argument goes off the rails. You say it as if the girls are being given a reward or financial incentive to be pregnant. The money is not for the girls. The money is for the child and paid to whoever is repsonsible for the child. If the child were taken away from its mother the mother would reeive no child support.

It is a very socialistic Idea. It is just like the idea of Universal Health care.
The child, as a British citizen, has the right to food, shelter, healthcare, education and justice. To my mind that is not socialist it is the noble and right path to follow. The concept of nobless oblige, which requires the haves to help the have nots, was around well before socialism. And the concept of charity and helping those less fortunate is to be found in all the great religions of the world and has been with us for a couple of thousand of years.

So who dig the pit? Socialists did it.
I am fairly confident that the rich man who hates paying tax and always votes right wing would get his bean counter to work out that injections cost less than child support payments. The idea of injecting contraceptives to prevent unwanted prregnancy is, I suspect, a policy that right wing parties and voters could support.

How you make the leap from the injections to socialists baffles me. Yes, it may have been introduced by the Labour Party but calling the New Labour Party socialist is like calling the Democrat Party socialist.

The religious socialism exclaimed sacrifice of Good Man in favour of the guilty one
The measure is for the purpose of reducing the burden on the good man not to increase it. The good man is texed less by the cost of injections than child support. And don't forget the child support is not for the guilty mother but the innocent child.

Socialism never works and it always causes havoc
You mean never works like the cradle-to-grave social care in Sweden, a country in havoc. And if socialism never works howcome voters re-elect the Labour Party. Come to that howcome the socialist parties even exist. The answer is because the black-white concept of socialist or capitalist is invalid. No party or government is socialist or capitalist, they are a mixture ot the two. The blend changes with the times and this mix is precisely what the voters decide on in elections.

Also, after being injected, girls will think that ‘Nothing can happen to me because I can’t get pregnant" and that attitude will obviously be dangerous
Yes there is a danger of that but I think the injections are given to girl who are going to do i anyway so its a case of damage limitation rather than preventing under-age sex. And the argument that it is wrong because it may lead to a "nothing can happen to me" attitude is invalid. By that logic we should ban crash helmets or seat belts because the wear may take that attitude and be encouraged to drive recklessly!

The parents hold minimal rights over their kids. They even cannot smack them.
If children are brought up to think that if you are angry with somebody or somebody does wrong then the solution is to resort to physical violence then the danger is clear. Cases of assualt will inevitably rise and should that kid grow up to be a leader he may think that attacking a country for not complying with rules is the solution.

Mr Frearson, who is separated from the boy's mother, found his son in a park 10 minutes later and smacked him once. But a passer-by reported it to Plymouth police and four officers arrived at his house, took him away and locked him in a cell awaiting questioning.
Well done passer-by. Just imagine she did nothing and next day she reads about a boy abducted from the park because a man threatened to smack him again if he did not get into his car.

We don't know all the details of this case. The man may not have been charged. He may have been kept overnight to cool down rather than sending him home to his kid in a rage. Yes probably he is a decent father but how are we to guard against child abuse if we cannot detain and intervew those hitting their son. And maybe if those policemen had been brought up thinking that smacking is the way to stop people breaking rules they would have smacked the father about instead of putting him in a cell!

I think you are making a mountain out of a molehill with this injection controversy. Yes it is a debateablle topic but to make it the argument against the evils of socialism or that epitome of socialism Jesus Christ is off the mark. And what may happen if there is no injection or child support. Babies in plastic bags dumped in trash cans or begging on the streets as is often the case in less developed countries without the safety net of a "socialist" welfare system. What solution would you propose to the problem of unwanted pregnacy.